Kadee #234 Draft gear boxes.
#234 HO Scale Short Shank Coupler Plastic Gearboxes & Lids
Plastic Draft Gearboxes & Lids included with 20-Series (#23, 24, 25 short shank), 40-Series (43, 44 & 45 short shank) Couplers. Also works with short shank Whisker® Couplers.
10 pair per package
2-56 screws are the most commonly used for center hole.
0-48 or 0-80 screws are used for side holes.