- All
- Product Name
- Product Keyword
- Product Model
- Product Summary
- Product Description
- Multi Field Search
Views: 0 Author: TOPBOLT technical team Publish Time: 2026-10-27 Origin: Site
Uppercase letters represent internal threads, lowercase letters represent external threads. Numbers indicate tolerance grade. Smaller grade number means tighter tolerance bandwidth.
6H: Standard internal thread tolerance, zero fundamental deviation, widely used for nuts and tapped holes, typical for DIN934 hex nuts.
6g: General external thread tolerance, reserved clearance for normal electroplating, commonly adopted by DIN933 hex head bolts.
5g6g: Dual-tolerance external thread, pitch diameter controlled to grade 5, major diameter controlled to grade 6. Overall fit is tighter than 6g.
Tolerance Match | Fit Feature | Suitable Scenarios | Coating Risk |
|---|---|---|---|
6H/6g | Standard medium clearance fit, default commercial fastener combination | General bolts, studs, common assembly | Suitable for regular zinc plating with thin coating |
6H/5g6g | Tighter fit, smaller clearance between mating threads | Precision equipment, low vibration, high repeatability assembly | Low tolerance for plating thickness, easy out-of-tolerance after coating |
Buyers treat 5g6g as an upgraded version of 6g and directly replace it in general purchase orders. The drawing requires 6H/6g while the supplier delivers 5g6g, or vice versa. Even if the thread looks visually identical, the ring gauge or plug gauge will fail during inspection.
Zinc plating, zinc flake and other surface treatments add material on thread flank. 6g has extra built-in allowance for coating absorption. 5g6g tolerance zone is narrower. After plating, the pitch diameter quickly exceeds upper limit, GO gauge cannot be screwed in, and the whole batch is rejected by third-party inspectors or client site QC. This problem frequently occurs for matched sets of DIN933 bolts and DIN934 nuts.
If the supplier uses 6g ring gauge for production inspection but the overseas inspector uses 5g6g gauge, qualified goods from factory will be judged non-conforming at destination port. Gauge class must match the tolerance specified on purchase order.
Correct marking example: M12×1.75-6H/6g or M12×1.75-6H/5g6g. Tolerance class must be written completely, not simplified. When ordering paired fasteners, fill in full tolerance marks for DIN933 bolts and DIN934 nuts in your inquiry and purchase order.
If external threads will be electroplated, confirm the reserved allowance before plating. 5g6g is not recommended for thick coating jobs. For heavy plating requirement, select 6e or 6f tolerance class.
Request the supplier to provide gauge calibration certificate. The GO/NO-GO ring gauge and plug gauge must correspond exactly to the tolerance class in the contract.
Mistake 1: Assume 5g6g is higher quality and use it for all general fastener orders.
Mistake 2: Only mark thread size without tolerance class on inquiry sheet.
Mistake 3: Ignore coating influence, specify 5g6g then carry out conventional zinc plating.
Mistake 4: Factory inspection gauge and customer incoming gauge adopt different tolerance standards.
Q1: Can 6H/5g6g replace 6H/6g directly? A1: Not recommended. 5g6g has tighter pitch diameter tolerance. If there is plating, replacement will greatly increase non-conformance risk. Only use it when the drawing clearly requires precision fit.
Q2: If goods already failed gauge test after plating, is rework feasible? A2: Rework by chasing thread is possible, but it will remove coating and affect corrosion resistance. Most overseas projects refuse reworked threads for critical connections.
Q3: Does 5g6g mean stronger bolt? A3: No. Thread tolerance only controls dimensional fit, and it has no relation with mechanical strength grade such as 8.8, 10.9 or A2-70.
