The approximately 2.8mm (.110”) parallel gap when holding the key, ensures that you can grip the full range of woodwind arms without marking parts by pinching or slipping.
#27’s polished stainless-steel surfaces allow contacting the key without blemishing its fine finish, be it plated, lacquered, or precious metal.
The leather offers great security because the “give” of the leather conforms to the key with a surface that will hold the part even better than the smooth polished jaw.
Maintaining your J.L. Smith #27 Pliers: Over time, particles from metal finishes will be attracted to the polished jaws of the pliers. To keep doing your best work, maintain the jaw surfaces. Polish the jaws occasionally with Tripoli on your buffing machine. This will restore the surface of the pliers to their original luster and takes less than a minute.