Oajen caster socket furniture insert for 5/16" x 1-1/2" stem, use with 5/8" OD round tube, 4-pack Caster socket for caster with 5/16" x 1-1/2" socket stem (grip neck). 4-pack. Made in Taiwan. Caster socket to go into 5/8" OD round tube 18 gauge. Caster socket OD 15.5mm / 0.610"