Note: If this part is exactly what you need, fine. Otherwise, I have created a customizable version of this here

This is a part that was in a design my kids found on the Internet but wasn't in any of the dozens of Lego(tm) sets they had. I measured a similar part with calipers and used a little guesswork, and the resulting part seems to work in their build.

It sliced in MakerBot Desktop and printed on a MakerBot Replicator 2 using the exact dimensions provided, but if your printer has shrinkage on interior spaces or wobbles you might have to increase the tolerances in OpenSCAD. It prints in under 5 minutes (including hot end warmup) so you can experiment easily.

Doesn't Matter

Doesn't Matter

0.2mm

10%

The part is generally very forgiving, but the inset/sink around the middle hole is a 0.8mm right angle overhang. Remove it on the bottom side if you have any problems in that area.