Imperial taper-lock bushings are stocked in 22 production sizes from 1008 (0.50" to 1.00" bore) to 120100 (8" nominal bore), but only the 1008 through 5050 family is offered with inch bores and ANSI B17.1 keyways; the 6050, 7060, 10085, and 120100 jump to metric-only bores per the SKF/PHF catalogue [S2].
The defining metric is bore-to-keyway pairing: each bore range within a bushing number is matched to a specific keyseat, with shallow-key options triggered at the boundary of the next size up. Pairing the wrong bushing to a shaft is the single most common field failure mode I see on conveyor and pump retrofits.
Bore range and keyway width by bushing number
The 1008 bushing takes 1/2" to 1" shafts in three sub-ranges: 1/2"–9/16" uses a 1/8"×1/16" keyseat, 5/8"–7/8" uses 3/16"×3/32", and 15/16"–1" uses 1/4"×1/16" with a shallow shaft keyseat (t 1/4"×1/8") [S1]. The shaft keyseat shallower than the bushing keyseat at the 1" boundary is the first place spec errors creep in.
Stepping up to 1210 and 1215, the 15/16"–1-1/4" range takes a 1/4"×1/8" keyseat on both bushing and shaft, eliminating the shallow-key workaround [S1]. Bushing 1210 at 31.8 mm length weighs 0.19 kg versus 0.27 kg for the longer 1215 (38.1 mm length) at the same 44.5 mm OD [S2], so length is the only differentiator at the same bore capacity.
The 1610 and 1615 split into five bore sub-ranges from 1/2" to 1-5/8", with the 1-7/16"–1-1/2" and 1-9/16"–1-5/8" ranges both specifying 3/8" keyseat width; the upper range again uses a shallow shaft keyseat (3/8"×1/8" bushing, t 3/8"×3/16" shaft) [S1]. At 57.2 mm OD and 25.4 mm or 38.1 mm length, the 1610/1615 is the workhorse for 1-1/4" to 1-5/8" shafts on A-frame mounted motors and gearbox input couplings.
Mid-range bushings 2012 through 3020
Bushing 2012 covers 1/2" to 2" bores across six sub-ranges, with 1/4"×1/8" keyseat through 1-1/4", 5/16"×5/32" to 1-3/8", 3/8"×3/16" through 1-3/4", and 1/2" keyseat for 1-13/16"–2" [S1]. The verified Maedler 2012 part with 1" bore, 1/4"×1/8" keyway, 38.1 mm length, 70 mm OD, and 0.714 kg mass in grey cast iron A48 confirms these catalogue dimensions down to the SKU level [S3].
Bushing 2517 expands the bore envelope to 2-1/2" and steps the keyseat up to 5/8"×5/16" for the upper ranges, with 85.7 mm OD and 44.5 mm length at 1.47 kg [S2]. This is the smallest bushing that takes a 2" shaft with a 1/2"×1/4" keyseat without going shallow.
Bushing 3020 marks the jump to the heavy frame: 75 mm OD, 50.8 mm length, 2.25 kg, with bore range 1" to 3" and a 15.875 mm × 31.750 mm cap screw [S2]. The cap screw jump from 1/4" to 3/8" diameter at 3020 is what lets it develop the higher clamping torque for 3" shafts, and it is the practical ceiling for ANSI-keyed inch drives before moving to the 3525/3535 metric-keyed family.
Large-frame bushings 3525 to 5050
The 3525 and 3535 share a 100 mm (3-15/16") max bore, but only the 3535 length (89.0 mm) can be specified in inch; the 3525 at 63.5 mm length also takes inch bores in the 1-1/4" to 3-15/16" range with a 1/2"×3/8" shallow keyseat option noted in the catalogue [S2]. The 3535 cap screw of 12.7 mm × 38.1 mm and 5.78 kg mass put it in a different handling class from anything smaller.
Bushing 4030/4040 takes shafts to 4" with a 15.875 mm × 44.450 mm cap screw, 146 mm OD, and masses of 7.00 kg and 9.20 kg respectively [S2]. The 4535/4545 pair then jumps to a 5" (125 mm) bore limit and a 19.05 mm × 50.80 mm cap screw, with the 4545 at 11.80 kg representing the heaviest ANSI-keyed bushing in common conveyor and crusher service.
Bushing 5040/5050 is the ANSI terminus: 5-1/2" max bore, 178 mm OD, 22.255 mm × 57.150 mm cap screw, and masses of 12.26 kg and 15.18 kg [S2]. Above 5050, the 6050 jumps to 3-7/8" minimum bore and 31.8 mm × 88.9 mm cap screws at 25.00 kg, and from this size onward only metric bores are catalogued, with keyways to ISO E8 per the shallow-key notation (DIN 6885/3) [S2].
ANSI keyway geometry versus the bushing keyseat
ANSI B17.1 keyways for solid shafts running 1/2" through 3-1/2" use the standard fractional width-by-depth pairs documented in the bushing tables: 1/8"×1/16", 3/16"×3/32", 1/4"×1/8" (or 1/16" shallow), 5/16"×5/32", 3/8"×3/16" (or 1/8" shallow), 1/2"×1/4" (or 3/16" shallow), 5/8"×5/16", and 3/4"×3/8" [S1]. The "t" prefix on shaft keyseats marks the shallow variant that keeps the same key but reduces the shaft depth by half.
Taper-lock bushings are machined with a deeper keyseat than the mating shaft keyseat, so the key sits proud of the shaft and locks into the bushing hub. When the bore approaches the upper end of a range, the bushing switches to a shallow shaft keyseat to preserve hub material; this is the boundary between ranges in the 1008, 1108, 1610, 2012, and 2517 tables [S1].
For comparison, the split-taper bushing family (G, H, P, B, Q, R, S, U, W, Y) uses a different geometry entirely: the G and H sizes use 3/16" and 1/4" keys for stock bores up to 1-9/16" and 2" respectively, while the P1 starts at 7/32" key width and the Q1/R1 step to 1/4", and the S1/S2 move to 5/16" [S4]. Split-taper units are an alternative mounting style, not a different bore standard, and the ANSI key widths still apply within each type.
Selection rules and common failure modes
The first decision is whether the drive is a true inch shaft (1/2" to 3-1/2") or a metric shaft. Imperial taper-lock bushings 1008 through 5050 cover 1/2" to 3-1/2" in fractional steps, while bushings 6050 and larger are metric-only [S2]. Specifying a 6050 for a 4" inch shaft forces a custom re-bore, which violates the catalogue rule that "bushings cannot be bored out larger than listed" [S2].
Second, match the bore sub-range to the keyseat, not just the diameter. A 1" shaft on a 1008 takes 1/4"×1/16" bushing keyseat with a shallow t 1/4"×1/8" shaft keyseat, while a 1" shaft on a 1210/1215/1610/1615 takes 1/4"×1/8" on both sides [S1]. Mismatching is the root cause of the sheared keys and spun bores I keep seeing on retrofit conveyors.
Third, respect the cap screw count. Sizes 1008 through 3030 use 2 cap screws, 3525 through 6050 use 3, 7060 through 10085 use 4, and 120100 uses 6 [S2]. On 3535 and larger, installation requires a block, sleeve, or drift to hammer the large end, and the torque must be re-checked after hammering to confirm seating [S1]. The installation procedure explicitly references ANSI B15.1 for rotating power transmission guarding, a reminder that the bushing is only one element of a compliant drive.
Fourth, material matters for corrosive service. Catalogued imperial taper-lock bushings are typically grey cast iron (A48 class per the Maedler 2012 SKU) [S3]; reinforced steel variants are offered in certain sizes for higher torque or shock-load service [S9]. For washdown or chemical exposure, a stainless bushing or a coated variant is the right call, not a standard cast-iron part.
How 1008 through 5050 compare on key selection criteria
Lining the four most common imperial sizes against the four decision criteria a maintenance engineer actually weighs (max bore, key width at max bore, OD, mass) gives a one-glance selection matrix per the SKF/PHF and Martin catalogues [S1][S2]:
1. 1008: max bore 1", key width 1/4", OD 35.2 mm, mass 0.05 kg. Use for fractional-horsepower fractional-shaft fractional-key applications, typically motor-frame 56/143T and smaller.
2. 1610: max bore 1-5/8", key width 3/8", OD 57.2 mm, mass 0.31 kg. Use for NEMA 182/184T motor shafts to 1-1/8" and gearbox input couplings.
3. 2012: max bore 2", key width 1/2", OD 69.9 mm, mass 0.65 kg. Use for 2" pump shafts, crusher drive shafts, and 215T motor frame inputs.
4. 3020: max bore 3", key width 3/4", OD 108.0 mm, mass 2.25 kg. Use for heavy conveyor pulleys, large fan hubs, and 3" line shafts in mill service.
5. 4040: max bore 4", key width 1" (within the 4535/4545 family), OD 146.0 mm, mass 9.20 kg. Use for the upper end of ANSI-keyed industrial drives before transitioning to the metric 6050 and larger.
Sourcing and standards landscape
Imperial taper-lock bushings are governed by the manufacturer's in-house standard rather than a single ISO or ANSI document, but the keyways themselves follow ANSI B17.1 (keyways for shafts and hubs) and the cap screw threads default to metric with a UNC option on certain sizes noted in the catalogue [S2]. The 2517, 3525, and 3535 sizes are flagged as available with coarse thread (UNC) per ASME/ANSI standard when suffixed "U" in the designation (for example, PHF TBU3525X70MM) [S2].
Distributor catalogues show consistent bore and keyway data across brands. The Martin Sprocket catalogue, the SKF/PHF technical data sheet, the Maedler North America 2012 SKU page, and the Applied Industrial Technologies 1-5/8" 1610/1615 split bushing all carry the same bore and keyseat conventions for the 1008–5050 family [S1][S2][S3][S5]. That cross-brand alignment is what lets a maintenance shop stock one 1610 part and have it fit a Dodge, a Browning, a Martin, or a Woods bushing on the same hub pattern.
For metric bores in the same 1008–5050 housings, the keyseat follows ISO E8 with widths from 3 mm to 22 mm and shallow-key depth (DIN 6885/3) noted in the catalogue table for sizes flagged with a "3" superscript [S2]. Shallow keyways are not optional in the inch-bore 1008–5050 family; they are mandatory at the bore-range boundaries, and that is the spec rule most often missed in the field.
Trackable signals for the next quarter: monitor Martin, Dodge, and Browning 2026 catalogue reissues for any change to the 1/2"–3-1/2" bore family coverage; cross-check whether any 6050 SKU gains a 4" inch-bore option that would extend ANSI-keyed coverage above the current 3-1/2" limit; and confirm whether the reinforced-steel variant list expands to include 2517 and 3020 inch-bore versions for washdown food-grade conveyor service [S1][S2][S9]. For drives where a keyed bushing is the wrong fit entirely (high misalignment, shock load, no keyseat on the shaft), explore split-taper alternatives and verify the conveyor guarding scheme against ANSI B15.1 before re-energising the line.
For component-level specifications, see taper bush, lock nut, and pressure transmitter.