3/8"-16 to 1/2"-13 x 1-1/4" Zinc Plated Steel Coarse Thread Rod Coupling Nuts

Diameter: 3/8"
Diameter 2: 1/2"
Length: 1-1/4"
Material: Steel
Finish: Zinc
Driver Type: 11/16" Wrench
Thread Size: 16 (Coarse)
Style: Reducer
Type: Coupling Nut

Box of 6.

A coupling nut is a long nut tapped from each side to meet in the middle, rather than all the way through in the same direction, used to connect two threaded rods end to end.