I recently made a cross-slide lock for my lathe. Half way through the project I found out I needed to replace the carriage lock because it was interfering with the cross-slide lock. My lathe originally had a simple setup: an M8 socket head cap screw in the carriage pulled a cast iron block up against the front way when tightened. This worked fine initially, but I quickly tired of digging through swaf to find the proper Allen key.
Below is the second version of my locking screw( the first one worked, but isn’t as pretty). The clamping bolt is essentially a stainless M8 bolt with a custom head. The handle is a section of stainless turned to a diameter of 5.5mm and then tapped on each end for a M4 socket head cap screw. Since the heads of the screws are slightly larger than the hole in the clamping bolt, the handle can slide from side to side without falling out.