4 in. Square Head Rail Bolt (3/8 in.) click image for larger view $9.75 each Product #: BOLT/SQ4 Add 4" square head rail bolt - length under head, 3/8" with 16 threads per inch (for finer thread slate nuts). Head is tapped for 10/32" screw for rosette. Comes with heavy duty washer. You may also be interested in… Square Nut for Rail Bolt with 16 threads per inch $2.50 each Results 1 - 1 of 1