These commercial grade heavy-duty inside corners should be used with one of the outside corners.

Available:

Inside Corner, 8-1/4"L x 5"H with square holes, Part # 26401

Inside Corner, 8-1/4"L x 5"H with elongated holes, Part # 26417 (Image Shown Above)

Inside Corner, 10-1/2"L x 5"H with elongated holes and larger brace, Part # 26424

Hardware is designed for use with 1-1/2" thick lumber (minimum width 6"). All standard hardware is mounted with 3/8" carriage bolts, (Part # 26534).  Use 1/2" carriage bolts (Part # 26535) on commercial grade.  All male and female dock-to-dock connections are made with 3/4" bolts with lock nuts or or 3/4" connecting pins.