This listing comes with one Extension Clamp.
"These tube extender clamps are used for combining two shorter bars to make one long bar. Allowing you to connect two 1 ½" diameter rack tubes end to end.
Please note: We ask that you don't use this clamp in a horizontal setting which means: don't use it to connect two horizontal bars together because if you start adding weight to the bar, wherever this clamp is, there will be a weak spot."
See what Gibraltar has to say about a variety of their clamps in the video below. At 6:57 he demonstrates the Extension Clamp specifically.
WARNING: Cancer and Reproductive Harm - https://www.P65Warnings.ca.gov