What size bolt is required for a hole drilled to .3750?

To determine the appropriate bolt size for a hole drilled to .3750 inches, it's important to understand the standard bolt sizing system, particularly for aircraft fasteners. The AN series bolts are identified by their nominal diameter, which corresponds to the hole they are intended to fit.

The size of the bolts in question corresponds to their nominal diameter in inches:

• AN3 bolts have a diameter of 3/16 inch (0.1875 inches).

• AN4 bolts have a diameter of 1/4 inch (0.250 inches).

• AN5 bolts have a diameter of 5/16 inch (0.3125 inches).

• AN6 bolts have a diameter of 3/8 inch (0.375 inches).

When looking at the size of the hole, a hole drilled to .3750 inches requires a bolt that closely matches this diameter. The AN6 bolt, with a diameter of 3/8 inch, is the only bolt size that fits a .3750-inch hole. This size provides the correct fit and ensures that the bolt can be securely fastened without excessive play or requiring a larger, incompatible diameter which could compromise the integrity of the fastening.

In summary, the AN6 bolt is the size required for a