These are Great Planes Brass Threaded Inserts (6-32).
FEATURES Brass construction The perfect way to put threads into wood and mount engines to wood mounting rails. Threaded inserts make a simple & effective way to make wing hold downs. Can be used where blind nuts are hard to fit Comes in a Parts-Pak clear plastic box with resealable lid
INCLUDES (4) Threaded Inserts
SPECIFICATIONS Thread Size: 6-32 Length: 5/16" Diameter: 7/32" OD overall 5/32" OD of main body
COMMENTS Package says it threads into a ¼" hole. But it threads into a 3/16" diameter hole that is 5/16" deep.