| 摘要 |
<p>A fastener head having a pair of recesses formed therein, a ledge in each recess being located a short distance axially below the head surface and extending a predetermined angular length from the axial portion of the ledge. The dimension of the ledge is adjustable to accommodate the strength of the fastener material in a manner such that the displacement formation of recess material on the surface of the fastener head is prevented during normal installation procedures. The drive angle on the recess is designed to be zero degrees.</p> |
