Gear Replacement Is Not a "Close Enough" Game
Gears must mesh correctly or they will tell you about it — loudly. Noise, vibration, heat, and accelerated wear are all symptoms of mismatched tooth geometry. Two numbers decide whether a replacement gear will work: diametral pitch and pressure angle.
Diametral Pitch (DP)
Diametral pitch is the ratio of the number of teeth to the pitch diameter in inches. It defines tooth size. A 4 DP gear has larger teeth than a 16 DP gear of the same pitch diameter. Stock spur gear catalogs — like the one RBC carries — list gears from coarse pitches (3DP, 4DP) through fine pitches (20DP, 24DP) in standard tooth counts.
Critical rule: two meshing gears must have the same DP. Mixing pitches produces interference, rapid tooth wear, and eventual failure.
Pressure Angle: 14.5° vs. 20°
Pressure angle is the angle of the tooth face relative to the line of action. Older equipment commonly uses 14.5°; modern industrial gearing standardizes on 20°. The 20° tooth is stronger and handles higher loads; the 14.5° tooth has a larger contact ratio and quieter operation at light loads.
- 14.5° gears: match legacy equipment and existing 14.5° mates.
- 20° gears: the default for new and replacement industrial drives.
Warning: a 14.5° gear and a 20° gear of the same DP look similar but will not mesh correctly. Always verify pressure angle before ordering — measure with a gear tooth caliper or check the original equipment manual.
Bore, Keyway, and Material
Beyond tooth geometry, match the bore diameter, keyway size, and hub style (plain, one-side, or two-side hub). Stock steel gears handle most industrial loads; bronze gears are specified for corrosion resistance or compatibility with hardened steel mates; made-to-order gears cover odd tooth counts, special bores, and non-standard materials.
When to Order Made-to-Spec
If the tooth count, DP, or pressure angle falls outside stock offerings — or the gear is part of a matched set — a made-to-order gear is the right call. Modern gear cutting holds the accuracy needed to replace even legacy OEM gears without modifying the rest of the drive.
Related catalog item: RBC Industrial carries stock spur, bevel, miter, worm, and gear rack products, plus a full gear catalog with DP, tooth count, bore, and keyway data. We can also cross-reference made-to-order gears to your sample or print.
Send us your gear sample, print, or nameplate data — we will identify the DP and pressure angle before you order.