On a linear motion stage the timing pulley is the rotary-to-linear coupling: it converts servo torque into belt-driven carriage travel, and every field on its RFQ line either fixes a gear ratio, a torque limit, or a fitment tolerance, so missing fields cascade into requote cycles [S1][S3].
Scope of this article: a process engineer's walkthrough of the six lines that must appear on the pulley line of the BOM (pitch, tooth count, bore and keyway, belt width, material and finish, flange and mounting style), plus the trap fields that suppliers silently default when the RFQ is silent [S1][S4][S7].
Line 1: Tooth Pitch and Profile Family
ANSI inch pitch designations 0.080 in MXL, 0.200 in XL, 0.375 in L, 0.500 in H, 0.875 in XH, and 0.250 in XXH bracket the standard light-to-heavy duty envelope, with MXL, 40-DP, XL, and L pitched parts classed as light duty and H/XH/XXH as the heavy end [S1].
For metric stages, the matching families are T2.5, T5, T10, AT5, AT10, and the high-torque P8M profile, where the prefix letter codes trapezoidal (T) or curvilinear (HTD/RPP) tooth geometry and the number is the pitch in mm [S3][S4][S6]. Pick the profile by belt manufacturer first: Gates PowerGrip GT3, Conti Synchroflex, and B&B all map to different series, so the RFQ should name the belt manufacturer and part number, not just the pitch code [S6].
Mismatch between pulley and belt profile is the single most common requote trigger on linear-stage RFQs; a T-series pulley will not mesh with an AT-series belt, and an HTD pulley will not seat a T-series belt cleanly [S6].
Line 2: Tooth Count, Pitch Diameter, and the Resulting Resolution
Tooth count sets pitch diameter (PD) through PD = pitch x teeth / pi, and on a linear stage the carriage travels one belt pitch per tooth-pass, so a 20-tooth T2.5 pulley yields 2.5 mm of linear travel per revolution and a 40-tooth T10 pulley yields 10 mm per revolution [S3][S4].
For a target linear resolution of 0.05 mm/rev at the encoder, the pulley must be sized so the servo encoder PPR divided by tooth count lands on the desired µm/step figure, and this relationship is what forces buyers toward 20, 24, 30, 40, 48, 50, or 60-tooth catalog values rather than free choice [S3][S4]. Available tooth counts on the T2.5 and P8M catalogs span 14 to 60 teeth, with 20, 40, and 60 as the standard stocked values and the rest cut-to-order [S3][S4].
Small-pitch pulleys under 20 teeth run a higher risk of belt-tooth jumping under shock load and are usually avoided on vertical or acceleration-critical stages [S1][S3].
Line 3: Shaft Bore, Keyway, and Tapped Holes
The bore and keyway block is the field that suppliers re-quote on most often: the T2.5 catalog alone lists seven bore variants (H round, P round + tap, N new JIS keyway + tap, NK new JIS keyway 10 mm with 4 mm x 1.8 mm key, C old JIS keyway + tap, V stepped, F counterbored) and twelve bore diameters from 4 mm to 14 mm, with 6.35 mm as the fractional option [S3].
The P8M high-torque series limits bore diameters to 12 to 42 mm with explicit shaft-bore code 00, and ships in a keyless bushing mount so phase-matching is done at the bushing rather than at the bore, which removes the keyway decision entirely from the RFQ [S4]. Specifying the wrong keyway standard (JIS old vs new vs ISO) is a top-three cause of pulleys arriving with a keyseat that does not match the motor shaft, and the fix is a new bore [S3].
For a linear stage driven by a NEMA 23 or NEMA 34 stepper, 6.35 mm (1/4 in), 8 mm, 10 mm, and 12.7 mm (1/2 in) are the bores that will land without a custom charge from the major catalog houses [S3][S4].
Line 4: Belt Width, Flange, and the Linear-Motion Interface
Belt width on inch pitch parts is given in inches (1/8 in, 3/16 in, 1/4 in up to about 2 in), and on metric P8M high-torque parts it is given in mm with 15 mm and 25 mm as the standard catalog widths and 50 mm, 100 mm as build-to-order [S4][S6].
Belt width is the torque knob on a linear stage: doubling belt width roughly doubles the torque capacity for the same pitch and tooth count, because shear area in the belt tensile cord doubles, and this is why wide-format stages (gantry, long-travel pick-and-place) move from 25 mm to 50 mm or 100 mm P8M rather than stepping up to a larger pitch [S4][S6].</h2> <p>Flange options on the T2.5 and P8M lines include NFC, RFC, and LFC (no flange, raised flange, lowered flange combinations), and these flange codes are not reflected in the supplier's CAD download, so the stage designer must hand-edit the STEP file or request a drawing before the pulley ships [S3][S4].
Line 5: Material, Surface Treatment, and Balancing
Catalog materials for high-torque metric pulleys are aluminum and aluminum alloy 7000 series (Duralumin), with surface treatments of black oxide, clear anodize, hard clear anodize, and electroless nickel plating, and each treatment moves both corrosion resistance and friction coefficient against the belt tooth [S4].</h2> <p>Aluminum 7075-T6 is the default high-torque choice on P8M at 25 mm and 50 mm belt widths; the MXL/XL/S2M/S3M/S5M bar-stock configurator on the other end of the catalog lists a 0.13 in (1/8 in) wide bar stock pulley as the standard light-duty configurable width, with the buyer cutting to length on the shop floor [S7][S4].
For cleanroom or medical stages, hard clear anodize is the default finish because it does not shed aluminum oxide the way black oxide can; for washdown or food-grade stages, electroless nickel plating is the typical upgrade, at roughly 2x to 3x the cost of the bare-aluminum part [S4].
Line 6: Standards, Compliance, and the RFQ Fields That Get Re-Asked
RoHS status is a yes/no flag that the catalog does not always print on the product page: P8M pulleys are RoHS non-compliant only when the BMC alteration is selected, and RoHS-compliant when BMC is not selected, so the RFQ must state which side of that branch the buyer is on, otherwise the default is non-compliant and the assembly line stops at the compliance gate [S4].
For automotive timing-belt idler and tensioner pulleys (a related but different commodity), catalog fields include OE cross-reference, model fitment, and material, with the Honda 14510-PTO-003 reference part for F22B/F23A engines 1997 to 2002 a representative example of the depth of cross-reference data the automotive idler market carries [S2].
The six lines above are the ones that survive a sourcing-engineer review without a re-quote; every other field (hub length, set-screw position, anti-rotation tap, dowel pin, dynamic balance grade) is a build-to-order addition that should be flagged explicitly on the RFQ or it will be omitted from the quote.
Trackable next signals for a sourcing team watching this commodity: the S14M profile now appears alongside H and L in the metric/inch filter for high-torque linear stages, suggesting suppliers are extending heavy-pitch stock for long-travel gantries [S6]; the configurator-width bar-stock option (BMXL13) gives a same-day-ship path for prototype stages where a 1/8 in bar can be cut to any face width on the shop floor [S7]; and large-format catalog houses continue to publish P8M at 145 part numbers and T2.5 at 82 part numbers, a coverage breadth that lets a buyer pin a single supplier for an entire prototype [S3][S4].
For the relevant spec sheets and selection criteria, see linear motion, and motion controller.
For related coverage, see Rebar Cutter Selection for Concrete Work: Capacity, Power, and Blade Gates.