A
coupling for mechanically connecting modular tubular struts of a positioning apparatus or
space frame, comprising a pair of toothed rings (10, 12) attached to separate strut members (16), the teeth (18, 20) of the primary rings (10, 12) mechanically
interlocking in both an axial and circumferential manner, and a third part comprising a sliding, toothed collar (14) the teeth (22) of which
interlock the teeth (18, 20) of the primary rings (10, 12), preventing them from disengaging, and completely locking the
assembly together. A secondary mechanism provides a nesting force for the collar, and / or retains it. The
coupling is self-contained and requires no external tools for installation, and can be assembled with gloved hands in demanding environments. No gauging or measured torque is required for
assembly. The
assembly can easily be visually inspected to determine a “go” or “no-go” status. The
coupling is compact and relatively light-weight. Because of it's triply
interlocking teeth, the connection is rigid. The connection does not primarily rely on clamps, springs or friction based fasteners, and is therefore reliable in fail-safe applications.