I required some simple stops for my t-track system without clamps, and came up with these two designs. The hole is an attempt to reduce filament usage and print times. 

While the corner stop does not stay in place very well without a clamp, it does the job at lining something up square if held in place.

This is for a universal t-track system. Dimensions for the slot are 11mm (base), 5mm (channel?). Scale ever so slightly if you require a tighter fit.

• Printed with ABS, but any filament type will suffice.
• No supports required if oriented as shown in pictures.
• Mirror the corner stop in your slicer for opposite angle.