Understanding Clearance Holes
A $\mathbf{clearance\ hole}$ is a hole slightly larger than the diameter of the fastener (screw or bolt) being used. This extra space (the clearance) is necessary to allow for:
- **Ease of Assembly:** Quickly aligning and inserting the bolt without forcing.
- **Manufacturing Tolerances:** Accounting for slight variations in the bolt's diameter and the hole's position.
- **Thermal Expansion:** Allowing for slight movement due to temperature changes.
Fit Tolerances Explained
The amount of clearance added depends on the required precision of the assembly. The calculator uses the following typical industrial standards:
Close Fit (Tightest)
Used when alignment and location accuracy are critical. Requires careful positioning of the bolt and may require a light tap to insert. **Minimum clearance.**
Normal Fit (Standard)
The most common choice for general engineering applications. Allows for easy assembly by hand while maintaining reasonable positional accuracy.
Loose Fit (Easiest)
Used when generous alignment is needed, often with long assemblies or for coarse construction. Allows for significant positional shift (float) of the bolt.
Drill Bit Selection Note
Matching to Standard Bits
The calculated hole diameter may not perfectly match a **standard fraction, number, or letter drill bit** in your set. Always select the **next largest standard drill bit size** available to ensure proper clearance.