Did you know that hub-pilot and ball-seat wheel-mounting systems don't mix? Serious problems such as premature wheel cracking, broken mounting studs and potential wheel failure can result if you install the wrong wheels on a vehicle.

Hub-pilot wheels center the wheel on the hub and have straight mounting holes with flat-faced nuts. Ball-seat, or stud-pilot, wheels center the wheel on the studs and have tapered mounting holes with chamfer-faced nuts. Some hub-pilot and ball-seat wheels have the same bolt circle diameter and number of bolts, so it's possible to mount the wrong wheels by mistake.

When replacing a wheel, always make sure the replacement has the same mounting system — the two systems won't work properly with each other, and the results can be disastrous.

This feature offers a variety of short tips and facts about apparatus maintenance and testing. Look for it every month. Submissions of 150 words or less are welcome from our readers, subject to editing. Send them to In Service Senior Editor Chris Cavette.