Makers participate in remixing culture by drawing inspiration from, combining, and adapting designs for physical objects. To examine how makers remix each others' designs on a community scale, we analyzed metadata from over 175,000 digital designs from Thingiverse, the largest online design community for digital fabrication. Remixed designs on Thingiverse are predominantly generated designs from Customizer– a built-in web app for adjusting parametric designs. However, we find that these designs do not elicit subsequent user activity and the authors who generate them tend not to contribute additional content to Thingiverse. Outside of Customizer, influential sources of remixing include complex assemblies and design primitives, as well as non-physical resources posing as physical designs. Building on our findings, we discuss ways in which online maker communities could become more than just design repositories and better support collaborative remixing.