Formula used
Recommended hole = Standard hole + process allowance + coating allowance + thermal allowance + positional allowance + safety allowance.
Diametral clearance = Recommended hole − nominal fastener diameter.
Radial clearance = Diametral clearance ÷ 2.
Removed volume = Hole area × plate thickness × hole count.
How to use this calculator
Choose a standard and metric fastener size. Then select the required fit series. Enter manual values only for custom work.
Add tolerances and manufacturing allowances carefully. Select the material, process, and hole geometry. Enter an available drill for suitability checking.
Press calculate to review the recommended diameter. Compare drill sizes and limits. Verify critical work with approved drawings.
Example data
| Fastener | Fine hole | Medium hole | Coarse hole |
|---|---|---|---|
| M3 | 3.2 mm | 3.4 mm | 3.6 mm |
| M4 | 4.3 mm | 4.5 mm | 4.8 mm |
| M5 | 5.3 mm | 5.5 mm | 5.8 mm |
| M6 | 6.4 mm | 6.6 mm | 7.0 mm |
| M8 | 8.4 mm | 9.0 mm | 10.0 mm |
| M10 | 10.5 mm | 11.0 mm | 12.0 mm |
| M12 | 13.0 mm | 13.5 mm | 14.5 mm |
| M16 | 17.0 mm | 17.5 mm | 18.5 mm |
| M20 | 21.0 mm | 22.0 mm | 24.0 mm |
| M24 | 25.0 mm | 26.0 mm | 28.0 mm |
Frequently asked questions
What is a clearance hole?
A clearance hole lets a fastener pass freely. It does not create threads. The mating component usually contains the thread.
How does a clearance hole differ from a tap drill?
A tap drill prepares material for internal threads. Its diameter is smaller than the fastener. A clearance hole is larger.
Which fit should I choose?
Fine fits improve location control. Medium fits suit general assembly. Coarse fits allow greater alignment variation.
Why do standards use lookup tables?
Standard sizes follow preferred engineering series. They are not produced by one universal formula. Tables preserve approved dimensions.
Can I use the nearest drill size?
Yes, when it remains within tolerance. Check the calculator status first. Consider drill runout and process variation.
What does clearance per side mean?
It is the radial gap around the fastener. It equals half the diametral clearance. Centered assembly is assumed.
Why add coating allowance?
Coatings reduce the final open diameter. An allowance can compensate for plated surfaces. Confirm the coating process thickness.
When should I use a slotted hole?
Slots allow movement or assembly adjustment. Their direction should match the needed movement. Structural rules may restrict slots.
How accurate is drilling time?
The time is an estimate only. Real feed, pecking, tool wear, and setup matter. Verify production planning separately.
Can this calculator design safety-critical joints?
No calculator replaces engineering approval. Loads, fatigue, edge distance, and standards still matter. Use certified design procedures.
Can I enter inch values?
Yes, select inches before entering dimensions. The calculator converts everything internally. Results remain available in chosen units.