I recently found myself in the market for a bipod and settled on a Harris, not a knockoff, and opted for the 6″-9″ with a swivel. I must say finding information on the bipods was almost painful. I settled on the HBRMS which is spring loaded and has notches for 1″ increments. There is also the HBRS which is not spring loaded and does not have notches, but is the exact same price. There are options without the swivel and with longer legs, but for my purposes a 6″-9″ will work just fine.
Anyway, the Harris HBRMS comes with a knurled knob which is very difficult to grasp. For that reason there are many aftermarket pivot lock handles. After dropping the coin on the bipod, I really did not want to spend much on a pivot lock handle. After reading some Amazon reviews I settled on the Caldwell which at the time was $9.99. It is made for their Harris knockoff, but also comes with an SAE adapter which fits the Harris. Putting it on was a cinch. You remove the nut on the Harris with a 1/4″ socket or nut driver and after removing the knob, thread on the SAE adapter. Then put on the handle and using an allen wrench, 2.5mm IIRC, tighten down the screw for the handle. After that you are ready to roll. It took longer to find the tools in the toolbox than to change out the knob for the handle. I especially like that I can lift the handle if I need to reposition it to make it tighter or looser.
Anyway, if you need a handle for a Harris bipod with a swivel I recommend the Caldwell. The price is right and it only takes a few minutes to install!