hard-to-find fastener hard-to-find fastener 1/4-20 hard-to-find fastener washer hard-to-find fastener hollow wall hard-to-find fastener hollow wall 3/8 x 3-3/4 hard-to-find fastener nut hard-to-find fastener screw post hard-to-find fastener set screw hard-to-find fastener m12 hard-to-find fastener 5/16