This standard recommends the use of the number 3 square neck, 80-DEG round countersunk head and the number 7 reverse key, 60-DEG round countersunk head plow bolts for new designs. It includes standards on number 3 square neck, round countersunk repair head, number 4 countersunk, square repair head, number 6 heavy key, round countersunk repair head, and number 7 reverse key, round countersunk repair head for service purposes. Dimensions of the number 4 countersunk square regular head and the number6 heavy key, round countersunk regular head are given in the appendix, as information supplementing but not forming a part of this standard.