The pivot arm in our wheel chair locking mechanism is very important. It makes sure that the arm that reaches out to lock in stays out of the way while in use. 

When first figuring out how this locking mechanism was going to work we started with the motion we wanted it to have. After that I looked for product on the market that could do give us the motion we wanted. Two things I had in mind were pvc pivot arm joints and the adjustable poles that use spring clips.