This is a highly specialized clasp, designed by Kate McKinnon for her beadwork bracelets, and now carried exclusively by US! The basic idea is that you make two pockets for the clasp to slip into, and it functions like a spring - but it is easier to understand if you check out the additional pictures (from her book). Actual dimensions are: 23 x 38 mm - 9 mm wide at the two bars.

By the each.