Sliding Tee

[STEVETERRY]

A fixture mounting device for sidearms that adapts, at a right angle, the 1/2" schedule 40 (or sched. 80) pipe of a sidearm to the 1/2-13 mounting stud of a theatrical fixture.

http://www.bhphotovideo.com/c/product/389076-REG/Altman_TEE_Sliding_Tee_Cast_Iron.html