Shackle Dimensions for the 37D are 15/16"x 7/16" ideal for securing trailers, cables, and chains. Shackle dimensions for the 605, 1/4"x 1/2"x 3/4". Shackle fits openings 1/2" or larger; shackle guard is removable to accomodates 9/32" opening. The 605 has a built in anti-sawing pin.