Taper lock bushes feature a split through the entire bushing, a nominal 8° taper (1 11/16" per foot, or 14,06 %) on the outside diameter, and locking via blind hex socket-head screws that drive the bushing into the bore of the mating component, compressing the inner diameter onto a keyed shaft [S2].
The visual difference is the screw pattern: H-type is a 4-bolt, twin half-shell design with bolts spaced 90° apart, F-type is a 2-bolt, single-split pattern with bolts diametrically opposed (180°). This geometry, not the material, drives the torque capacity and bore-range distinction [S2].
Where the H and F codes come from
Taper-Lock is a registered design traceable to MPTA-B9i-2013, which sets the general dimensions and tolerances for detachable taper-lock bushings and their mating hubs in the 1008 through 120100 series [S2]. The two letter families inside that standard are not interchangeable. A QD bushing will not seat in a Taper-Lock hub, and a Taper-Lock bushing will not seat in a QD hub, because the taper angles, bolt patterns, and mounting geometries are different [S4]. The same rule applies between the H and F variants: the screw-circle diameter, the cap-head thread, and the through-split orientation all change between families, so a hub machined for F will not clamp correctly with H screws torqued in.
For readers new to the broader bushing taxonomy, the parent taper bush family also includes QD (Quick Disconnect), ST (Split Taper), and XT (Extra Taper) [S2][S5]. Among those, only the Taper-Lock and Double Split Taper (H/G type) lines share the 8° self-locking wedge geometry, while QD and ST use different angles and external flange features [S1][S5].
Bore range and series mapping
The four-digit Taper-Lock code encodes bore and length, and it applies equally to F and H series inside each numeric family. Common series and their imperial bore ranges run from 1008 at 1/2" through 1" up to 5050 at 1-3/4" through 5" [S4]. A 2012 in the F family covers 1/2" to 2" bores; a 3525 runs 1" to 3-1/2" [S4].
The H family is the heavier line in the same catalog numbering. F-type 2-bolt bushes typically cover series up to roughly 3030, with two 5/8-11NC through-bolts on a 4.00" bolt circle for 3020/3030 [S2]. H-type 4-bolt bushes appear at the same numeric step but use a different bolt-circle geometry: for example the 3525/3535 step moves to a 4.83" bolt circle with 1/2-13NC screws, and the 4545 step uses a 6.13" bolt circle with 3/4-10NC screws [S2]. That 4-bolt circle is the engineering reason H-types can carry higher axial clamping load and larger bore diameters within an equivalent OD envelope.
Clamping mechanics and shaft tolerance
Both H and F bushes lock by the same wedge principle. Screws pull the bushing axially into the hub's tapered bore, the taper converts that axial pull into radial compression, and the resulting hoop load grips the keyed shaft [S2][S3]. The 8° self-holding angle is shallow enough that the joint will not back-drive under vibration, but steep enough that hand-tool torque on the cap screws generates a useful radial preload [S2].
Shaft tolerance is the most common source of installation problems, not the H/F choice. Design call-out is h9 on the shaft, and the joint will clamp and grip across roughly +0.051 mm / -0.127 mm of deviation from nominal [S3]. An oversize shaft at the high end of that band can make the bush very tight to slide on before the screws are torqued; undersize shafts reduce contact pressure and can mark the shaft under load [S3]. In practice, light filing of high spots or a flat-blade wedge opened in the bush slot is used to get the assembly onto the shaft, with no grease on the tapers or on the retaining screws, since lubricant on either surface drops the friction coefficient the wedge needs to develop its grip [S3].
Selection: when H pays for itself, when F is enough
Use F-type when the driven component is small, the bore is in the lower half of the catalog range, and reversing or shock loading is rare. The 2-bolt pattern halves the assembly time, fits where a 4-bolt pattern would not clear a hub web or spokes, and is sufficient for most fractional-horsepower conveyor, fan, and light pump couplings. [S3]
Use H-type when any of the following apply: bore above roughly 2-1/2" (series 3020 and up), reversing duty, frequent start-stop cycles, keyless hubs in high-torque service, or any application where the catalog specifies a 4-bolt bushing rather than a 2-bolt one. The twin half-shell clamping spreads the radial preload more evenly around the shaft, which reduces the localized hoop stress that cracks 2-bolt bushes when they are over-torqued or pushed past their bore range. Compare the two against four common decision criteria below.
Note the cross-system rule: H and F are not substitutes for each other inside the same hub. A Taper-Lock hub bored and drilled for an F bush cannot be converted to H by re-tapping, and a lock nut or external key is not part of either design, so any perceived slip should be diagnosed as a hub/bush mismatch, screw torque drift, or shaft tolerance issue, not as a missing fastener [S4].
Installation and removal specifics
For both H and F bushes, the working sequence is: clean shaft and bore, key the shaft, slide the bush into the hub, hand-tighten the cap screws until the bush just seats, then torque in a star or alternating pattern to the catalog value [S7]. On 3535 and larger, use a block, sleeve, or drift against the large end of the bush to drive it out, never a hammer directly on the bush body, because direct impact chips the cast iron flange and throws the taper out of spec [S7].
Removal is the reverse: back the screws out evenly to walk the bush out of the hub, and lift the driven component off the shaft. If the bush has seized in the hub (typically because grease reached the tapers at install), apply a penetrating oil at the split line and re-tap screws alternately rather than driving the bush out with a pry bar, which will distort the taper and scrap the bush [S3][S7].
Common failure modes and how to read them
Cracking along the split after a short service life almost always traces to one of three causes: grease on the tapers at install, an oversize shaft that forced the bush to clamp from an already-stressed state, or a 2-bolt (F) bush pressed into a 4-bolt (H) duty cycle [S3]. Slip on the shaft without visible cracking is a different signature: it points to a hub/bush mismatch, an under-torqued screw (very common when one of the four H-pattern screws is missed), or a worn keyway on the driven component [S3][S4].
For deeper coverage of the 8° wedge geometry and its relation to the broader bushing family, the reference page on taper bushes walks through the wedge action, the MPTA-B9i-2013 dimensioning rules, and the stainless variants used in food and beverage service [S2]. Readers comparing the F/H choice to other shaft-locking methods should also weigh the maintenance profile against a lock nut arrangement, since nut-on-shaft joints tolerate more axial thrust but require a longer shaft engagement and a different removal procedure [S4].
Trackable signals to watch over the next catalog cycle: any MPTA-B9i revision that re-tables bore ranges at the 3020/3030 and 3525/3535 steps, since those are the transition points where F runs out of headroom and H takes over, and any movement of H-type 4-bolt bushes into the smaller 2012/2517 series, which would compress the F family's remaining niche in fractional-horsepower drives.
The underlying component specifications are covered under dry type transformer.
This topic is covered further in Ejector vs Tipping Body for Low Overhead: 2026 Spec Map.