Summary

A lightweight, adjustable clamp for gluing small parts.

Instructions

Adjustable spring clamp.
Uses a clothespin spring like these others do:
http://www.thingiverse.com/thing:307551
http://www.thingiverse.com/thing:677020

This one can span anything up to about 6 inches (150mm). Jaw depth is near 2.25 inches.

The arms get jammed when clamped, and won't slip.

There's a little bit of flex, but not much.
It turned out great on the first attempt. The "arm" sections were a smooth, sliding fit, and I didn't want to mess around making things thicker for more stiffness. It's really not needed for holding small pieces together as glue dries.
I'd guess the clamp applies about one pound (1/2 kilo) of pressure.

A complete set of 4 pieces (2+2) required 49 minutes, 25 grams ABS using 0.3mm layers at normal speed.

I'd go with 0.3mm layers or finer for smooth surfaces. A touch of sandpaper may be beneficial to the fit.

Metric versions included.

Clamp adjustable clothespin spring