This End Splice Clamp is an excellent solution for end-to-end gluing and assembly of parts. An opening in the clamp allows you to glue to parts together while they're clamped in place, guaranteeing they won't move before the glue sets.

Overall length: 150mm. Overall width: 75mm. Clamping surface: 85mm long x 20mm wide in two places. I used M4 bolts and brass inserts. I recycled a mouse pad for the non-slip surface on the clamp. The nuts on the longer bolts at the back of the clamp are used to keep the two surfaces parallel. 

I am using knobs from Nils Kal:

https://www.printables.com/model/21935-metric-clamping-knobs-m4-m5-m6-m8/files