How to Read a Chinese Agricultural Parts Technical Drawing

How to Read a Chinese Agricultural Parts Technical Drawing

Chinese agricultural parts technical drawings follow the GB/T (Guobiao) national standard, which is based on the ISO drawing standard but differs from the ANSI/ASME system used in North America and from the BS 308 system used in the United Kingdom. For agricultural equipment buyers sourcing parts directly from Chinese manufacturers, being able to read and verify a technical drawing is a critical skill — it allows you to confirm that the part you are being supplied matches the specification you need, catch dimensional errors before parts are manufactured, and communicate changes clearly without relying entirely on the supplier’s interpretation of your verbal description.

This guide covers the key elements of Chinese agricultural parts drawings that commonly differ from Western drawing conventions, how to interpret the most important dimensions and tolerances, and what to verify before approving a drawing for production.

Chinese agricultural parts drawings follow GB/T standards — understanding the key differences from Western conventions prevents costly interpretation errors in production.

First-Angle vs Third-Angle Projection

The most immediately confusing difference between Chinese and Western technical drawings is the projection method. Chinese drawings use first-angle projection (consistent with ISO and European practice), while North American drawings use third-angle projection. In first-angle projection, the front view is placed top-left, the top view is placed below the front view, and the right-side view is placed to the left of the front view — the opposite of the third-angle convention that places the right-side view to the right. A drawing symbol in the title block identifies the method: a truncated cone symbol with the small end facing right indicates first-angle; small end facing left indicates third-angle. Always check this symbol before reading dimensions from views.

Dimension Tolerances and Surface Finish

Chinese drawings express dimensional tolerances following GB/T 1800 — the fundamental tolerance standard aligned with ISO 286. Tolerances appear as letter-number codes: H7 for a hole, h6 for a shaft. The capital letter indicates a hole (internal feature) and the lowercase letter indicates a shaft (external feature). The number indicates the tolerance grade — lower numbers are tighter. Common fits in agricultural parts: H7/h6 is a close clearance fit used for gear bores and shaft shoulders; H8/f7 is a looser clearance fit for less critical locations. If you need to convert a tolerance code to an actual dimensional allowance, use the tolerance tables in GB/T 1800.2 or the equivalent ISO 286-2 — both are available from Chinese standards bodies and international standards organisations.

Surface finish is expressed as Ra (arithmetic mean roughness) in micrometres, written as the Ra value inside an inverted triangle symbol. Ra 3.2 μm is a machined finish; Ra 1.6 μm is a smoother finish typical of bearing bores; Ra 6.3 μm is an acceptable general machined surface. These values align with ISO and are directly comparable to Ra values on Western drawings.

Material Designations and Grade Equivalents

Key Items to Verify Before Approving a Drawing

Before approving a Chinese supplier’s drawing for production, verify: the projection angle is identified and you are reading views in the correct orientation; all critical dimensions match your specification (bore diameter, key width, flange bolt pattern, overall length); tolerances on functional surfaces are specified and are achievable in the supplier’s process; material grade is specified on the drawing title block, not just discussed in email; heat treatment specification (carburising depth, hardness range) is noted on the drawing if applicable; and surface finish is specified on bearing surfaces and sealing surfaces. Request a first-article sample for dimensional verification against the drawing before committing to volume production.

PRR Tractor Part Limited Partnership has extensive experience in sourcing agricultural parts directly from Chinese manufacturers. Browse our gearbox catalog и каталог снаряжения, or contact [email protected] for direct sourcing assistance.

Часто задаваемые вопросы