These spacers are molded in NY 6 material in hex shape to give better grip while tightening. Hex af is suitable to fix in standard nut drivers. Length starts from 6 mm upto 85 mm in M3 and M4 threding with 6mm, 8mm and 10mm AF. (O.D.) Spacers are molded with brass inserts and M.S. Screw. Many combinations like Male + Female, Female + Female, Male + Male are available as per customers requirements. Very useful to mount two pcbs or pcb and chasi. Also useful to mount acrylic sheets in control panels.