Knob for old sliding glass door

Good afternoon, Erik.

It appears you have an old Keller/Air Control patio glass door; that company has gone out of business and the lock is no longer manufactured. With that being said, there is no exact replacement for this lock. What normally breaks on the lock is the interior mortise latch, not the outside turn handle. Here's how to check: remove the handle and try turning the inside mortise lock with a screw driver to see if the latch will lock.

Personally, what I have done in the past as far as replacing the lock was to use the 82-005 Surface Mounted Lock.