This is the American Model Builders HO Scale Wheel Paint Mask Acrylic Kit for 36" WalthersProto/Life Like Proto 2000 Wheels.
These paint masks are precision cut to fit popular high quality HO scale wheel sets. It not only keeps paint off of the wheel treads leaving just the front and back wheel faces and axle exposed for color, but keeps the modeler's hands clean as well.
American-Models Product Number: 911
Walthers Product Number: 152-911
Walthers Catalog: 2015 HO, page 175
The mask will hold four axles and, once painted, each of its "fingers" can be individually pulled apart to release one wheel set at a time. Unlike cardboard masks, these will last for years! The mask is easy to assemble from 5 clear acrylic parts; a plastic solvent glue, such as Creations Unlimited's Plastic-I-Weld, is all that is required.