This listing is for a pair of Gibraltar Memory Locks.
"Slip on memory locks are designed to be used at the knuckles of the rack, which means the joints. They have a male tab that fits into a female cutout which locks the bar into the same position every single time that also adds stability."
Diameter: 1 1/2"
All Metal Construction
Watch this video from Gibraltar talking about these locks:
WARNING: Cancer and Reproductive Harm - https://www.P65Warnings.ca.gov