Why do the end caps fit loosely when placed inside the tubing?

Ways to get end caps to fit securely

Bar foot rail end caps are designed to fit loosely to allow room for error during manufacturing. Simply slide your end cap into the end of the tubing to attach it. We recommend coating the inside of the end of your tubing with an adhesive, such as Loctite Red or JB Weld SuperWeld, before inserting the end caps for a permanent bond. You can also wrap the stem of the end cap with masking tape or electrical tape several times before sliding it into the tubing for a snug fit.