+/-.010
Ruland Fcr20-6-6-A Coupling, 6 Beam Clamp, Bore 3/8 X 3/8 In
Rounded corners includes rivets, so it sits flat and stays put during use.
Ruland Pcr16-6-6-A Coupling, 4 Beam Clamp, Bore 3/8 X 3/8 In
For straightforward reliability, I always lean toward the WILTON brand.