I recently bought a pair of cheap parallels from MSC, and after about 1 month of use, many of them have become warped. I'm trying to determine whether this is because I bought a POS product, or because of something I've done wrong.

When I clamp a work piece in my vice using the parallels, I'll tap the piece down with a rawhide hammer to ensure that there is no clearance. I wouldn't expect this to warp a piece of hardened steal, but who knows.

Anyone experience a problem like this before? These are the parallels in question, fyi

1/8 In. Thin Style, 10 Pair Parallel Sets - Thin Parallel Sets | MSCDirect.com