GT2 pulley 17T with shaft coupler, flag

This is one answer to the question, "how do you compare the outputs of two optoencoders with 6mm shafts, turning at the same speed?" This tube couples two 6 mm shafts end to end, with a 17 tooth GT2 (2 mm) timing belt pulley in the middle, and a flag for an optointerrupter at one end. OpenSCAD file provided.