A 3020 taper lock bushing covers a 3 inch maximum bore at a 2 inch axial length, and a 2517 covers 2.5 inch bore at 1.75 inch length, while the Q1 sits in the QD bushing family with a 1.15 inch maximum bore at its largest size [S6][S7][S1].
The naming overlap between the two systems is the most common source of cross-spec errors: a "3020" is a Taper-Lock part with a 30/20 bore/length code, whereas a "Q1" is a single-digit-letter QD code tied to flange-bolt count and barrel length, not a bore/length split [S6][S7].
Bore and length decoding on the 3020 family
The 4-digit Taper-Lock code is read as two paired numbers: the first pair is the maximum bore in inches, and the second pair is the axial bushing length in inches [S6][S7]. On a 3020 that resolves to 3.0 inch max bore, 2.0 inch length, with a documented bore range that climbs past 2-15/16 inch and approaches 3 inch depending on the manufacturer [S4]. The 2517 follows the same rule and resolves to 2.5 inch max bore at 1.75 inch length; 2517 also weighs 3.4 to 3.5 lb per bushing in the Martin catalog, giving a useful mass check at goods-in [S4].
Standard Taper-Lock bores from 1008 (1 inch max bore, 0.8 inch length) through 4040 (4 inch max bore, 4 inch length) are listed in catalog form, and keyseat dimensions on the bushing follow a different schedule than keyseat dimensions on the mating shaft: the bore-side keyseat is depth-compensated because the bushing has a longitudinal slit [S4]. A 2012 at 48 mm shaft size sits at the very top of its bore range, which is the practical reason most flywheel and crusher retrofit threads reference the 3020 instead, since 48 mm lands inside the lower end of the 3020 bore window rather than its ceiling [S5].
Where Q1 actually lives in the bushing taxonomy
Q1 is not a Taper-Lock designation. Q1 belongs to the QD (Quick Detachable) family and is distinguished by its straight-sided outside diameter intended to mount flush into a pocket-machined component, unlike a Taper-Lock that protrudes from the hub face [S1]. In distributor catalogs the Q1 sits next to Q2, R1, R2, H, and QT bushings as a separate SKU line, and is typically drilled and tapped to match a specific bolt circle for a given sheave or sprocket [S1].
The QD numbering convention uses a single letter that denotes barrel length family and a numeric series that maps to bore; a Q1 at its largest reaches 1-1/8 inch to 1-3/16 inch (around 1.15 inch) bore, well below the 3.0 inch ceiling of a 3020 [S1]. When a Taper-Lock 3020 is on the BOM, the equivalent QD part is several series up, often an R1 or R2 depending on bore and hub style, never a Q1 [S1]. For a broader map of how these families relate to split bushings and XTB, see the side-by-side comparison on split-taper, QD, and XTB bushing differences, which puts the families on a common axis of bore range, hub style, and removal effort.
Fit, tolerance, and shaft-size windows
Taper-Lock bushings are designed around an h9 shaft tolerance, but documented Fenner production limits allow a working window of +0.051 mm to -0.127 mm on the shaft diameter for the bore to slide on and clamp correctly [S5]. On a 3020 bored for a 48 mm shaft, measured diameters of 48.01 mm and 48.04 mm sit inside that window, but a build-up near the upper end noticeably increases the slide-on force because the taper slip is then smaller [S5].
Pragmatic workshop practice when the bushing is tight: open the slit with a flat blade or fox wedge, slide the bushing into the component, finger-tighten the cap screws, and only then drive the cap screws to torque; grease goes on the shaft and bore interface but not on the tapers or cap threads, since oil on the taper surfaces will hydraulically prevent the locking action from completing [S5]. A useful cross-check on the 3020 bore selection is the related question of how spacer hubs and endplay presets interact with bushing systems, which clarifies that bushing axial length sets the available clamp travel, not the bearing endplay window.
Decision matrix: 3020 vs 2517 vs Q1
Three criteria separate these parts cleanly: maximum bore, axial length, and bushing family. On bore, the 3020 reaches 3.0 inch, the 2517 reaches 2.5 inch, and the Q1 reaches about 1.15 inch at its top bore [S4][S1]. On axial length, the 3020 is 2.0 inch, the 2517 is 1.75 inch, and the Q1 is determined by the QD family barrel rather than the 4-digit code [S4][S1]. On family, 3020 and 2517 are Taper-Lock (flange bolts, protruding OD), while Q1 is QD (flange bolts, straight OD that sits flush in a pocket) [S1].
The selection rule reads: if the shaft is over 2.5 inch and you need Taper-Lock removable mounting, pick 3020; if the shaft is 1-7/16 inch to 2 inch, pick 2517 or 2012; if the shaft is below 1-3/16 inch and the component was designed with a pocket for a QD-style bushing, use a Q1, never a Taper-Lock 1xxx series, because the OD profile and bolt circle will not interchange [S1][S4]. The taper angle across all three families is the same 8 degree half-angle on the locking cone, so clamp behaviour is comparable; what differs is the OD geometry, the bolt circle, and how the bushing registers axially against the hub [S3].
Installation and removal on the 3020 and 2517
Installation per the Martin catalog: clean all oil, paint, and debris from the shaft, bore, and component pocket; align the hole pattern, not the threads, since each through-hole is tapped only on one side; thread the cap screws into the marked holes; alternately torque the cap screws in steps to the catalog value; on 3535 and larger bushings, drive the large end with a block or drift, never a hammer directly, then re-torque to confirm the reading has not drifted [S4]. Grease all unoccupied through-holes to keep debris out, and never use oil on the taper surfaces [S4].
Removal: take out all cap screws, move them to the holes marked on the bushing face, and alternately drive those screws to push the bushing back out of the taper [S4]. Re-installation follows the full 7-step procedure, including re-greasing of unoccupied holes [S4]. The catalog warning is unambiguous: rotating power transmission products must be guarded to ANSI B15.1, regardless of bushing family [S4].
When the 3020 is the wrong choice
The 3020 is the wrong pick when the component pocket is QD-drilled, when the shaft is below 1-3/16 inch, when the hub face lacks the axial room to seat a 2.0 inch long bushing, or when the application is a high-shock drive that has historically stripped the cap screws on 3020 size (some flywheel and stone-crusher retrofits have moved back to keyed bored-to-size hubs after repeated 3020 failures) [S5][S9]. It is also the wrong pick when the supplier is shipping from a region that treats Q1, H, and QT as a single interchangeable line, since those three are not dimensionally interchangeable even if the SKU looks similar at a glance [S1].
For designers cross-referencing part numbers across borders, the practical safeguard is to print the catalog page for the specific bushing family in use, the Martin interchangeable bushings catalog being a good baseline since it lists both metric and rebore dimensions in parallel [S2]. For a sanity check on adjacent tolerance issues, the article on piezoelectric vs screw-driven electric linear actuators covers a different but related question about how small dimensional errors propagate through a mechanical stack, and pairs naturally with the shaft-tolerance discussion above.
Track the following signals before committing to a 3020 in 2026 spec work: confirm the bore window from the actual shaft print rather than the nominal (3020 max bore is 3.0 inch, but the catalog lists it as 2-15/16 inch in some sources, so verify on the manufacturer's current data sheet); confirm hub face has at least 2.0 inch of clear axial length; confirm pocket drilling matches Taper-Lock bolt circle, not QD. If any of those three fail, the next candidate is a 2517 for bore up to 2.5 inch, or a bored-to-size hub with a standard key for higher torque density drives [S4][S5][S9].
For component-level specifications, see taper bush, lock nut, and pressure transmitter.