Think of the right drill bit size as the key that opens a secure grease fitting installation. When you’re working with a 1/4-28 grease fitting, precision is everything. Too large a hole compromises the seal, too small makes threading difficult.

You’ll want to use a #21 drill bit, measuring 0.159 inches, but there’s more to the process than just picking the size. Let’s explore what else you need to get this right.