C.E. Smith Adjustable Galvanized Keel Roller Brackets Pair - Mounts on any trailer tongue to hold a roller for keel support. Features: Offset bend: 1in Overall length: 11-1/2in Mounts with 3/8in bolts. Uses 5/8in dia roller shaft. Five height adjustment holes. Mounting: add 1in to tongue width to determine length of the two 3/8in mounting bolts. Roller: add 2in to tongue width to determine correct roller width. Shaft: add 3in to tongue width to determine 5/8in shaft length. Length determined by your roller and trailer tongue. Fasteners and roller not included.