Bell hanger bits (installer bits): sizes and lengths
A bell hanger bit is a long, slim twist drill with a small hole in the flute near the tip, called a fish eye or fish hole. You drill through a wall, stud, top plate, or floor, thread wire through the hole, and pull the wire back through the hole you just drilled, so one tool drills the passage and fishes the cable in a single pass [1] [2]. The same tool is sold as an installer bit, feeler bit, fishing bit, or wire installing drill bit, and the people who buy it are electricians, telephone and alarm installers, and low-voltage (data, CCTV, thermostat) contractors [1] [3]. This page charts the sizes: diameters from 3/16 to 1 in, overall lengths from 4 to 72 in, the shank quirks that decide what chuck you need, the steel variants, flexible installer bits as a separate animal, and what size to drill for Romex and 16-2 or 18-2 wire. For the rest of the wire-hole tool family, see wood boring bits compared; for standard twist drill length classes, see jobber drill bit sizes.
The one-minute answer
Three facts cover most questions. First, the mainstream is 1/4 to 1/2 in diameter by 18 to 24 in long: that crosses a typical stud bay or double top plate in one pass, and every maker in the chart below covers it [1] [2]. Second, shanks step down: at 1/2 in diameter and up, most makers turn the shank down to 3/8 or 7/16 in so the bit fits a smaller chuck [2] [4]. Third, material follows the wall: HSS for wood and the occasional nail, carbide-tipped once stucco, block, or metal lath is in the path, and cheaper carbon steel for pure wood-and-drywall work [1] [2] [5].
What it is, and who uses it
The design is a compromise tuned for one job: reaching through finished or semi-finished construction with the smallest possible hole. Standard drill bits keep diameter and length proportional to stay rigid; a bell hanger deliberately breaks that proportion, running 18 in and longer overall on diameters mostly between 1/4 and 1/2 in, so it can pass through an entire stud bay, a top or bottom plate, or a door frame and emerge with the drill still outside the wall [6] [1]. The fish hole near the tip is the distinguishing feature: after the hole is drilled, the wire is looped or hooked through it and pulled back through the wall, which is why the tool is also called a fishing bit [1] [4].
The trades on the package labels tell the story. ITM's catalog lists telephone installation, burglar alarms, and wire and cable applications [2]; ICS describes cable TV, telephone, alarm systems, and computer network wiring, and notes boatbuilders also use the bits for long bolt holes in stem, keel, and deadwood [1]; LH Dottie's spec sheet says telephone, security, and cable installations [5]. In practice that means electricians running NM cable through framing, low-voltage installers pulling HDMI, CAT6, coax, and sensor wire through finished walls, and HVAC techs dropping thermostat wire from attics [6] [7].
Bell hanger bit size chart (diameter x length)
The chart below is assembled from four manufacturer tables that list size, overall length, and shank together: ICS Cutting Tools' bellhanger extension drill matrix (HSS and carbide tipped), ITM's 308BH / 308CT / 308CS catalog page, LH Dottie's BLH class table, and B&A Manufacturing's BH series [1] [2] [5] [4]. Lengths are overall length (OAL) in inches. Where makers disagree on shank for the same diameter, both values are shown; that disagreement is real and is the point of the shank section below.
| Diameter | Typical shank | Overall lengths offered | Sources |
|---|---|---|---|
| 3/16 | 3/16 | 12, 18 (ITM, LH Dottie); 12 to 72 ladder (ICS) | [1] [2] [5] |
| 1/4 | 1/4 | 12, 18, 24, 30, 42 (ITM, LH Dottie); 12 to 72 (ICS) | [1] [2] [5] |
| 5/16 | 5/16 (ITM, LH Dottie, B&A) or 1/4 (ICS) | 12, 18, 24 (ITM, LH Dottie); 12 to 48 carbide (B&A); 12 to 72 (ICS) | [1] [2] [4] |
| 3/8 | 3/8 | 12, 18, 24, 30, 42, 48 (ITM); 12 to 42 (LH Dottie); 12 to 48 carbide (B&A); 12 to 72 (ICS) | [1] [2] [4] |
| 7/16 | 3/8 | 18 (ITM); 12 to 72 (ICS); 4 carbide (Magbit) | [1] [2] [3] |
| 1/2 | 3/8 (ITM, B&A) or 7/16 (Magbit) or 1/2 (ICS, LH Dottie) | 12, 18, 24, 30, 42, 48 (ITM); 12 to 72 (ICS); 4 to 30 carbide (Magbit) | [1] [2] [3] |
| 5/8 | 1/2 | 18 (ITM); 6, 12, 18, 24 carbide (Magbit); 12 to 48 (ICS) | [1] [2] [3] |
| 3/4 | 1/2 | 18 (ITM); 6, 12, 18, 24 carbide (Magbit); 12 to 48 (ICS) | [1] [2] [3] |
| 7/8 | 1/2 | 6, 18 carbide (Magbit); 12 to 48 (ICS) | [1] [3] |
| 1 | 1/2 | 6, 18 carbide (Magbit); 12 to 48 (ICS); 54 in flex-shaft variant (McMaster) | [1] [3] [8] |
Read the chart with three notes. First, the full 12 to 72 in ladder belongs to ICS, whose HSS matrix runs 12, 18, 24, 30, 42, 48, 60, and 72 in on the 3/16 through 1/2 in sizes and 12 to 48 in on the 9/16 through 1 in sizes [1]. ITM's HSS series tops out at 48 in, and its 5/8, 3/4, and 1 in diameters appear only at 18 in [2]. Second, the short 4 and 6 in lengths are Magbit's carbide-tipped 781 series, aimed at concrete screws in tight spots rather than wire fishing [3]. Third, a stocking dealer's range confirms the core of the chart: CDTooling summarizes its HSS bell hanger offering as 3/16 to 3/4 in diameter in 12, 18, 24, 36, and 48 in lengths [9].
One length is worth calling out because buyers ask for it by name: the 18 in x 3/8 in bit is the workhorse, carried by every maker in the chart and by low-voltage dealers like Tristate, which stocks ITM's 308BH series from 3/16 x 18 up to 1/2 x 18 alongside BES bellhanger bits [10] [2]. Stanley Supply lists the same 308BH series (3/16 x 12 through 1/4 x 42), a second listing confirming ITM's sizes [11].
The shank quirk: big diameters on small shanks
On ordinary twist drills the shank equals the cutting diameter up to 1/2 in. Bell hangers break that rule deliberately, stepping the shank down so a big bit still fits a 3/8 in chuck, which is what most installers carry [2] [4]. The pattern, maker by maker:
- ITM: 7/16 in on a 3/8 in shank, 1/2 in on a 3/8 in shank, and 5/8, 3/4, and 1 in all on a 1/2 in shank [2]
- ICS: 5/16 in on a 1/4 in shank, 7/16 in on a 3/8 in shank, and 9/16 through 1 in all on a 1/2 in shank [1]
- Magbit (carbide 781): 7/16 in on a 3/8 in shank, 1/2 in on a 7/16 in shank, 5/8 through 1 in on a 1/2 in shank [3]
- B&A: 1/2 in on a 3/8 in shank (its 1/4, 5/16, and 3/8 in sizes keep full-size shanks) [4]
- LH Dottie and ICS keep full 1/2 in shanks on their 1/2 in bits, the exception to the step-down habit [5] [1]
Practical upshot: do not assume the shank matches the diameter. Check the shank column before buying a 1/2 in bell hanger for a 3/8 in chuck, because ITM's and B&A's will fit and ICS's and LH Dottie's will not [2] [1]. LH Dottie's own spec page shows the confusion is built in: its BLH1224 (1/2 x 24) lists a 1/2 in shank but a 3/8 in chuck size in the same table [5]. For the chuck-capacity rules in general, see the drill chuck size chart.
HSS vs carbide-tipped vs carbon steel
Three steels cover the category, and the wall you are drilling picks the one:
- High speed steel (HSS) is the default. ICS's HSS bellhangers use a 118 degree special purpose point and are billed as drilling through wood plus nails and sheet metal encountered on the way [1]; ITM's 308BH HSS series makes the same wood-and-metal claim [2]. This is the bit for studs, plates, joists, and the occasional hidden fastener.
- Carbide tipped adds masonry to the path. B&A's BH series is tipped for stucco, masonry, concrete block, metal lath, wood, or any combination, and the maker notes the tip survives metal encountered while drilling [4]. Magbit's 781 series is tungsten-carbide tipped on a heat-treated body for brick and concrete [3], and ICS and ITM both list carbide-tipped bellhanger lines (CTBH and 308CT) with the same fish hole [1] [2]. McMaster sells the same construction under its wire-installation category [8].
- Carbon steel is the budget variant. ITM's 308CS series drills wood, studs, aluminum, insulation, and drywall at roughly half the HSS list price, with the explicit caveat that it will not perform like HSS in steel [2]. LH Dottie's BLH bits are listed as high carbon steel with a black oxide finish [5].
Point geometry varies more than the labels suggest: ICS grinds a 118 degree point on its HSS bits [1], while LH Dottie specifies an 82 degree drill point and a maximum of 800 RPM for its carbon steel bits [5]. Speed discipline matters on all of them: long thin bits whip and walk, so start slow, especially at the larger diameters [7]. For the coating and steel-family background (black oxide, titanium, cobalt), see drill bits by material; for masonry-specific drilling, the masonry bit size chart owns that family.
Flexible installer bits (a different animal)
Everything above is a stiff one-piece bit. A flexible installer bit puts a short, rigid cutting head (usually an auger-style screw point) on a long spring-steel shaft, so it can bend inside a wall cavity, be steered around obstructions, and drill from a small access hole; wire attaches to the fish hole at the tip exactly as on a stiff bell hanger [8] [12]. McMaster-Carr sells the archetype, Tru-Cut flexible-shaft bits for wire installation: 54 in overall (53 in max drilling depth) in 3/8, 1/2, 9/16, 5/8, 3/4, and 1 in cutting diameters, and 72 in overall (71 in depth) in 3/8, 1/2, and 9/16 in, all on slim 3/16 or 1/4 in round shanks, plus hand and ball guides that support and center the shaft between studs [8]. IRWIN's flexible installer bits cover the same ground: a 3/8 in x 54 in screw-tip version, a 1 in x 54 in auger version, and 1/4 in HSS-tip variants at 36 in, all with a wire-pulling hole in the flute and a 3-flatted shank that also accepts wire [12] [13].
| Cutting diameter | Overall length | Typical shank | Sources |
|---|---|---|---|
| 3/8 | 54 | 3/16 (Tru-Cut) or 3/8 3-flat (IRWIN) | [8] [13] |
| 1/2 | 54 | 1/4 (Tru-Cut) or 3/16 3-flat (aftermarket) | [8] [14] |
| 9/16 | 54 | 1/4 | [8] [14] |
| 3/4 | 54 | 1/4 | [8] [14] |
| 1 | 54 | 1/4 | [8] [13] |
| 3/8, 1/2, 9/16 | 72 | 3/16 or 1/4 | [8] [12] |
Flex bits trade rigidity for reach. Technique sources agree on the shape of the job: cut a small access hole (about 1/2 to 3/4 in) in the drywall, insert the head, aim across the cavity, and drill; the hole must be large enough for the taped wire connection to pass freely but as small as the finished wall allows [7]. Aftermarket 54 in bits in 9/16 and 3/4 in cutting diameters on 1/4 in shanks, with carbon steel heads on spring steel shafts, are widely listed and confirm the Tru-Cut size pattern [14]. Note what a flex bit is not: for long stiff runs through multiple framing members in open wood, a ship auger is the traditional tool, a comparison our wood boring bits page owns.
What size for pulling Romex and low-voltage wire
The hole has to pass two things: the cable and whatever you tape or hook to the fish hole. Guides converge on a simple ladder, with honest divergence at the margins:
| Cable or wire | Recommended diameter | Sources |
|---|---|---|
| Thermostat and sensor wire (18/2 to 18/5) | 1/4 to 5/16 | [6] [7] |
| Single CAT6, RG6, or other low-voltage run | 5/16 to 3/8 | [6] [7] |
| Single 14/2 or 12/2 NM (Romex) | 3/8 minimum, 1/2 common | [6] [15] |
| 12/3, 10/2, or two cables in one hole | 1/2 to 5/8 (guides range to 3/4) | [6] [16] |
| Connector-ended cable (HDMI with plug attached) | 5/8 to 3/4 | [6] [7] |
Two things to keep straight when you use the table. First, the 16-2 and 18-2 low-voltage wires themselves are thin; the reason installer guidance still starts at 1/4 to 3/8 in is that the fish hole is near the tip of a long thin bit, and a hole that barely passes the wire will not pass the loop or tape ball you pull it with, a point cable-bit guides make explicitly [7]. Second, the Romex recommendations genuinely diverge: drillbitsworld calls 3/8 in the minimum for a single NM cable with 1/2 in for bundles or heavier wire [6], toolsadvisers calls 1/2 in the most common size for 12/2 [15], and cohesivehomes pushes 9/16 in and up for easier pulling [17]; a long-running electricians' forum thread lands at 9/16 in for a single cable and 3/4 in for two [16]. Sizing up within the sources' range costs almost nothing in drilling effort and saves the re-drill.
Code framing matters more than hole diameter in studs: the forum thread and code summaries keep borings 1-1/4 in back from the stud face so drywall nails and screws cannot reach the cable, with nail plates required when you cannot [16]. And speed discipline applies: run the bit slow enough to control, since an 18 in bit that grabs will torque the drill hard [7]. For the pilot-hole sizes the screws in those studs want, see the pilot hole chart.
Related
For the wider wire-hole family (spade bits, Forstner bits, ship augers, hole saws): wood boring bits compared. For standard twist drill lengths and length classes: jobber drill bit sizes. For chuck capacity rules: drill chuck size chart. For bit steels and coatings: drill bits by material. For masonry drilling when the wall is block or concrete all the way through: masonry bit sizes and best drills for concrete.
Sources
- ICS Cutting Tools, catalog page 108, Bellhanger's Extension Drills plain and carbide tipped: HSS size/shank matrix 3/16 to 1 in with 12, 18, 24, 30, 42, 48, 60, 72 in lengths, 118 degree special purpose HSS point, fish eye (fish hole) description, aka names bell hanger, installer, feeler, fishing, skylight, spotlight bits, boatbuilding use, carbide CTBH series (icscuttingtools.com/catalog/page_108.pdf)
- International Tool Manufacturing (ITM), catalog page 48: 308BH HSS series (3/16 to 1 in, OAL 12 to 48 in, shanks listed per size including 7/16 and 1/2 in on 3/8 in shanks and 5/8 to 1 in on 1/2 in shank), 308CT carbide tip series (13 to 30 in), 308CS carbon steel series (1/4 and 3/8 in, 12 to 24 in, wood studs drywall insulation caveat), telephone / burglar alarm / wire and cable applications (itmtools.com/pdf-2013/ITM-p48.pdf)
- Magbit, Bell Hanger Carbide Tipped Drill Bit 781 series: cutting diameters 3/16 to 1 in, OAL 4, 6, 12, 18, 24, 30 in, shanks per size (7/16 in dia on 3/8 in shank, 1/2 in dia on 7/16 in shank, 5/8 to 1 in on 1/2 in shank), tungsten carbide tip for brick and concrete, fish eye hole (magbit.com, 781 series product page)
- B&A Manufacturing, BH Series bellhanger installer drill bits: carbide tipped for stucco, masonry, concrete block, metal lath, wood or combinations; 1/4, 5/16, 3/8 in on full-size shanks 12 to 48 in; 1/2 in on 3/8 in shank 12 to 48 in; flute fish hole for pulling wire (bamanufacturing.com/page_13.htm)
- LH Dottie, BLH bell hanger drill bits: class table 3/16 to 1/2 in x 12, 18, 24, 30, 42 in with shank sizes; BLH1224 spec page: high carbon steel, black oxide, 82 degree drill point, up to 800 RPM, one flute, 4-1/2 in flute length, telephone security cable applications, shank 1/2 in with chuck size 3/8 in (lhdottie.com/bell-hanger-drills/blh1224)
- Drill Bits World, Bellhanger Drill Bits category and electrical/HVAC pages: length-to-diameter design rationale, trade applications (NM Romex 14/2 12/2 14/3, low-voltage HDMI CAT6 RG6, thermostat 18/5), FAQ: 3/8 in minimum for single NM cable, 1/2 in for multiple cables or 12/3 and 10/2, occasionally 5/8 in (drillbitsworld.com/product-category/bellhangers/; drillbitsworld.com/industries/electrical-hvac/)
- Engineer Fix, How to Use a Cable Bit for Drilling and Wire Pulling: bit length selection 18 to 24 in single stud, 36 to 48 in multiple members, 6 ft for extreme runs; diameters 3/8 to 3/4 in with smaller sizes covering single-run low-voltage; access hole 1/2 to 3/4 in; hole sized to pass the taped connection (engineerfix.com/how-to-use-a-cable-bit-for-drilling-and-wire-pulling/)
- McMaster-Carr, Wire Installation Drill Bits: Flexible-Shaft Drill Bits for Wire Installation, Tru-Cut 54 in overall (53 in max drilling depth) in 3/8 (3/16 shank), 1/2, 9/16, 5/8, 3/4, 1 in (1/4 shank), 72 in overall (71 in depth) in 3/8, 1/2, 9/16 in; hand and ball guides; also known as bell hanger bits; HSS and carbide-tipped hollow-shaft wire installation versions (mcmaster.com/products/drill-bits/application~wire-installation-1/)
- CDTooling (Carbide and Diamond Tooling), Bell Hanger Feeler Drill Bits with Wire Fish Hole HSS category: diameters 3/16, 1/4, 5/16, 3/8, 1/2, 5/8, 3/4 in; lengths 12, 18, 24, 36, 48 in (carbideanddiamondtooling.com)
- Tristate Low Voltage Supply, Bellhanger Bits shop category: ITM 308BH HSS bits 3/16 x 18 through 1/2 x 18, ITM 1/2 x 12 fish hole, BES bellhanger bits 1/4 to 1/2 in x 12 to 24 in, retail stocking confirmation (tristatelvs.com/category/bellhanger-bits/shop)
- Stanley Supply, Series 308BH Bright Finish HSS Bell Hanger Feeler Bits with Fish Holes: ITM series listed 3/16 x 12, 1/4 x 12, 5/16 x 12, 3/8 x 12, 1/4 x 42 and up, US-made HSS wood and metal rating (stanleysupplyonline.com)
- IRWIN Tools, Flexible Installer Drill Bits: hole in flute for wire pulling, 3-flatted shank with wire hole, tapered flute, auger screw tip; HSS tip 135 degree self-centering split point stepped to 118 degree body; 1/4 in diameter SKUs at 36 in; product family page and distributor listings (irwin tools via mrosupply.com 1890947; amazon.com IRWIN flexible installer series)
- IRWIN 1890772 Flexible Installer Drill Bit with Screw Tip, 3/8 in, 54 in length; IRWIN 1890760 Flexible Installer Drill Bit with Auger Tip, 1 in, 54 in length (retailmarket.net; amazon.com)
- Aftermarket flexible installer bit listings, 54 in overall: 1/2 in auger with fish eye and screw point on 3/16 in 3-flat shank; 9/16 x 54 (HUAALIUCHE); 3/4 x 54 on 1/4 in shank with carbon steel head and spring steel shaft, includes guide ball kit (amazon.com flexible installer drill bit results; bestchoice.guide/installer-bits)
- Tools Advisers, What Size Drill Bit For 12/2 Romex: 1/2 in or larger recommended, 1/2 in the most common size for Romex, hole slightly larger than cable sheath (toolsadvisers.com/what-size-drill-bit-for-12-2-romex/)
- DoItYourself.com electrical forum, What size/brand auger bit to use for 12/2 and 12/3: 9/16 in for a single 12/2 or 12/3, 3/4 in for two cables, holes kept 1-1/4 in from stud face per code with nail plates otherwise, mid-joist drilling advice (doityourself.com forum thread 205094)
- Cohesive Homes, What Size Hole Need 12/2 Romex: 1/2 in acceptable, 9/16 in or larger recommended for easier pulling and protection, 3/4 in when running two or more cables (cohesivehomes.com/what-size-hole-need-12-2-romex)