The cotton grip head for our No. 520 Swivel-Lock Stretcher is recommended when stretching Berber carpets, loop pile carpets, and other low-level commercial carpets. The wire nap grips of this head are less likely to pull or snag loops or yarns that are easily damaged by the standard stretcher pin plate. Nap grip head for the Crain 520 Swivel-Lock Power Stretcher. Easily stretch cotton carpets without causing damage to loops. Nap grips are replaceable. Net weight: 4 lbs.