This is simlar to the Robjects concept. The idea is that this is one of a library of shapes that can be printed to help with the physical connection between prototyping components.
There will be more shapes uploaded in the future. They can all slot together and you use the pin model to then secure them.
Tolerates have been tested using a UP! printer and there is generally no slop or slack in the connections. If they are to tight let me know which printer and by how much and I can alter some derivative models
Update - 8/2/14
Added the source Blender file which contains the models I'm editing. Still very much a WIP but it is their to play with and make your own new blocks. I'll add more and more blocks progressively.
-Updated Servo Block Model (4A), corrected a few little things
-UPDATE: I've started making separate entries in Thingiverse for separate blocks, see the IRPB collection or just seach for Interconnecting Robot Prototype Blocks