Fits the MK7 and MK8 StepStruders.I didn't like the idea that the Delrin Plunger in the MakerBot Replicator was a wearable part that was destined to fail eventually, so I took out my plunger, measured it, and reproduced it in AutoCad. I printed it in PLA so that it would be sturdy enough to hold up for a while and so far, it has produced more than a dozen prints and it doesn't look to be any more worn out than when I first put it in. I put my original plunger in a safe place, and when this one wears out, I can just print another one.