This hex spacer is 1-7/8” long, 3/8” in diameter, and has #8-32 male threads on both ends.  It is used to mount most Stern plastic aprons (also referred to as arches).
Also used to mount the upper playfield in Stern's The Simpson's Pinball Party pinball machines.
Stern reference numbers 530-5285-00 & 530-5285-01.