Set of 8 sockets fits all number and fractional M.C.T.I. Standard taps thru 1/2". A lso fits 1/8" NPT taps and metric taps thru 12mm manufactured to M.C.T.I. standards. Sockets contained on a vinyl holder. PTI-SERT taps 4mm to 12mm metric / 4-40 to 1/2 inch. Sockets #1 thru #4 use 1/4 drive, rest use 3/8 drive.