I made this pan/tilt head to go on an arca rail clamp on my tripod. I was not able to get it to completely lock up completely because of the plastic-plastic friction but its good enough to hold its position with a spotting scope attached. In the future I may fix it with a tpu internal ring to increase lockup. All the hardware use is ¼-20 nuts and bolts. I happened to have a cam lever (in blue) laying around but a simple twist handle can be made for it as well. The cad is in a public onshape document so feel free to make yourself a copy and change some parameters as well. 

https://cad.onshape.com/documents/f4f84f0ce4d473c5c1f1b91d/w/7e591e58fe3c92e735150767/e/c0d4d778ea172adace0b146d