This is the Dual Swivel Ball Link 4-40 by Dubro.

Features

Plastic links for 4-40 sized rods

Includes

Two Dual Ball Link 4-40 Swivels
Two brass tapered collars
Two 3x15mm cap head screws
Two 3mm nuts

Specifications

Length: 1.7" (43mm)
Width: 0.39" (10mm)