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العربية A custom bolt drawing must give the supplier enough information to quote, manufacture, inspect, and pack the part correctly. A simple sketch with “M20 bolt” is not enough for production.
In real sourcing, many custom bolt problems come from missing details. The bolt shape may be clear, but the thread length, tolerance, material, grade, coating, or inspection requirement is not. That creates quotation delays, wrong samples, or failed assembly after delivery.
For drawing-based orders, buyers should treat the drawing as the main technical contract.
Basic Information Every Custom Bolt Drawing Needs
A custom bolt drawing should clearly define the geometry, material, strength, surface finish, and acceptance criteria.
| Drawing Item | What to Specify | Why It Matters |
|---|---|---|
| Product name | Custom bolt, anchor bolt, shoulder bolt, U-bolt, etc. | Defines the part type |
| Standard reference | DIN, ISO, ASTM, ANSI, or “made to drawing” | Helps compare with standard fasteners |
| Diameter | Nominal and actual critical diameter | Controls fit and strength |
| Overall length | Total bolt length | Affects assembly depth |
| Thread pitch | Metric, UNC, UNF, or special thread | Prevents nut mismatch |
| Thread length | Full thread or partial thread | Controls engagement |
| Head style | Hex, square, round, socket, special head | Affects tooling and clearance |
| Material | Carbon steel, alloy steel, stainless steel, etc. | Controls strength and corrosion resistance |
| Grade / class | 8.8, 10.9, 12.9, B7, A2-70, etc. | Defines mechanical performance |
| Surface finish | Zinc plated, HDG, black oxide, Dacromet, plain | Controls corrosion and thread fit |
Buyers can compare available standard fasteners before deciding whether a custom bolt is required.
Critical Dimensions to Mark
Thread and Shank Details
Thread information must be complete. Do not write only “M16” if the thread pitch is important.
Include:
- Major diameter
- Thread pitch
- Thread length
- Shank length
- Chamfer or thread start
- Thread tolerance if required
- Matching nut requirement
Head and Special Features
For non-standard heads, mark all working dimensions. This includes head height, across flats, socket depth, hole diameter, radius, groove, slot, bend angle, or welded feature.
If the part is not available as a catalog item, custom non-standard fasteners should be quoted with a complete drawing or approved sample.
Material, Grade and Finish Requirements
Material and strength should not be assumed from appearance.
| Requirement | Example |
|---|---|
| Material | 40Cr, SCM440, 304, 316, carbon steel |
| Strength grade | Class 8.8, 10.9, 12.9, ASTM A193 B7 |
| Heat treatment | Quenched and tempered, if required |
| Surface finish | Zinc plated, hot-dip galvanized, Dacromet |
| Test documents | MTC, hardness test, tensile test, inspection report |
For high-load applications, review high-strength fasteners and define mechanical testing before production.
Common Drawing Mistakes
Avoid these issues:
- Missing thread pitch.
- No tolerance on critical dimensions.
- Material listed but no strength grade.
- Coating not clearly defined.
- No matching nut or washer information.
- Drawing does not match the physical sample.
- Revision number missing.
- No inspection or certificate requirement.
For corrosion-sensitive applications, compare coated fasteners before confirming the finish.
Final RFQ Checklist
Before sending a custom bolt drawing, confirm:
- Drawing version and unit system
- Size, thread, head, and special features
- Material, grade, heat treatment, and coating
- Quantity and tolerance
- Application environment
- Required certificates and inspection reports
- Packaging and labeling needs
A good custom bolt drawing reduces guessing. It helps the supplier quote faster, produce more accurately, and inspect the final parts against clear requirements.