Jak zmierzyć moduł przekładni bez użycia specjalistycznych narzędzi

utworzone przez | cze 26, 2026 | Bieg

Agricultural Knowledge|PRR Tractor Part Limited Partnership|7 min read

Jak zmierzyć moduł przekładni bez użycia specjalistycznych narzędzi

Identifying the module of an unknown gear is one of the most common practical challenges in agricultural machinery maintenance — particularly when replacing gears in older equipment where service documentation has been lost, or when sourcing replacement parts from a supplier that requires a module specification rather than an OEM part number. The module can be determined accurately using a digital caliper and basic arithmetic, without a gear tooth caliper or optical comparator. The method works for any standard metric spur or helical gear with undamaged teeth.

This guide covers two measurement methods for identifying gear module, how to confirm the result, and what to do when the calculated value falls between standard module values.

how to measure gear module without special tools agricultural

Gear module can be determined accurately with a digital caliper and a tooth count — no gear tooth caliper or optical comparator required.

What Is Gear Module?

Module (m) is the fundamental parameter that defines tooth size in the metric gear system. It equals the pitch diameter divided by the number of teeth: m = d / z, where d is the pitch diameter in mm and z is the tooth count. Module determines everything about the tooth’s proportions — addendum, dedendum, tooth thickness, and root fillet radius are all defined as multiples of the module. Two gears can only mesh correctly if they have the same module and the same pressure angle. Standard modules follow the series: 1, 1.25, 1.5, 2, 2.5, 3, 4, 5, 6, 8, 10 — with 1 used only for very small instrument gears and 8–10 for heavy industrial drives. Agricultural gearbox gears typically fall in the 3–6 module range.

Method 1: Outside Diameter and Tooth Count

This is the most accurate method for external spur gears with undamaged tooth tips. The formula is: m = OD / (z + 2), where OD is the outside (tip) diameter measured across the full gear including the tooth tips, and z is the tooth count.

Step 1: Count all teeth around the gear and record as z. Count carefully — miscount by one tooth and the calculated module will be wrong.
Step 2: Measure the outside diameter with a digital caliper across two diametrically opposite tooth tips. Take three measurements at different positions and average them — a single measurement may land on a worn or damaged tip. Record OD in mm.
Step 3: Calculate m = OD ÷ (z + 2). Round the result to the nearest standard module value. If the calculated result is 3.97, the module is 4. If it is 2.48, the module is 2.5.

Example: A gear with 24 teeth and an outside diameter of 130 mm. m = 130 ÷ (24 + 2) = 130 ÷ 26 = 5.0. This is module 5.

Method 2: Span Measurement (Useful for Worn Gears)

When tooth tips are worn and outside diameter is unreliable, the span measurement method uses the measurement across a specific number of teeth with calipers closed on the tooth flanks rather than the tips. For a 20° pressure angle gear (standard for agricultural applications), measure across k teeth where k = z × 0.111 + 0.5 (rounded to nearest integer). The span measurement W = m × cos(20°) × (π × (k − 0.5) + z × inv(20°)), where inv(20°) = 0.01490. In practice, for a module 4 gear: W across 3 teeth ≈ 35.5 mm; for module 5 across 3 teeth ≈ 44.4 mm. Measure your gear and compare to the table for standard modules to identify the match.

Module OD per tooth (mm) Span over 3 teeth (20° PA, approx.) Common agricultural use
2 2.0 mm / tooth ~17.8 mm Metering mechanisms, small drives
3 3.0 mm / tooth ~26.7 mm Light gearboxes, tiller chain stage
4 4.0 mm / tooth ~35.5 mm Standard gearboxes, harvester heads
5 5.0 mm / tooth ~44.4 mm Medium gearboxes, baler drives
6 6.0 mm / tooth ~53.3 mm Heavy gearboxes, combine drives

What to Do When the Result Falls Between Standard Values

If your calculated module is, for example, 3.6, it is most likely module 4 with tip wear reducing the measured OD, or a non-standard module used by a specific manufacturer. Try the span measurement method as a cross-check — if the span measurement also points to a value between module 3 and module 4, the gear may be an inch-diametral-pitch gear rather than a metric module gear. In that case, calculate the equivalent DP: DP = 25.4 ÷ m. A calculated module of 3.17 corresponds to DP 8 — a very common inch-system gear size. Browse our agricultural gear catalog and contact our team with your measurement results for assistance identifying the correct replacement.

Agricultural Replacement Gears by Module and Tooth Count

PRR Tractor Part stocks spur, helical, and bevel gears in modules 2–8 for agricultural drives. Provide your measured OD, tooth count, bore diameter, and calculated module for a confirmed replacement.

Browse Gears →

Frequently Asked Questions

Does tooth wear affect the accuracy of the outside diameter method?+
Yes — tip wear reduces the measured outside diameter, causing the calculated module to appear smaller than the actual value. If the gear shows visible tip rounding or cupping, use the span measurement method instead, which measures across the tooth flanks rather than the tips and is unaffected by tip wear. Cross-checking both methods on a worn gear will typically bracket the true module between two standard values — the higher value is almost always correct.
Can I use this method on bevel gears?+
The outside diameter method works on bevel gears with a modification: measure the OD at the large end of the gear (the back cone end) and use the tooth count at that diameter. The module on a bevel gear is defined at the large end — the tooth tapers toward the small end (toe). The formula is the same: m = OD ÷ (z + 2), measured at the large end only.
Where can I source agricultural replacement gears once I have identified the module?+
PRR Tractor Part Limited Partnership stocks agricultural replacement gears in modules 2 through 8 for spur, helical, and bevel gear applications. Contact [email protected] with your module, tooth count, bore diameter, key profile, and gear type (spur, helical, or bevel). Browse current stock at our agricultural gear catalog.

Agricultural Gears by Module — Spur, Helical and Bevel

Module 2–8 in stock for agricultural gearboxes and implement drives — provide your measured specification for a confirmed replacement.

PRR Tractor Part Limited Partnership  |  [email protected]
304/1170 Soi Phahonyothin 49/1, skrzyżowanie 6, podokręg Talat Bang Khen, dystrykt Lak Si