A connector apparatus has a first portion and a second portion. The first portion mounts to an upright that has knobby hand grip protrusions. The second portion provides a connection for a laterally extending cross-member. The first portion interacts with the knobby hand grip protrusions to have a combination of a first degree of freedom permitting motion in one direction, while inhibiting motion in a second degree of freedom. The second portion has a releasable connection to the cross-member, and when engaged, has a degree of freedom of motion about an axis of the second portion cross-wise to the axis of the upright. The second portion has a releasable, retained, pin connector with a quarter-turn lock to prevent accidental disengagement. The connection of the second portion is offset such that when two connectors are seated back-to-back their cross-tie connections stand in substantially the same horizontal plane relative to the ground.