Is this part allowed in FTC?

[nicholsjj]

Ebay isn't considered a national retailer due to parts quickly going out of "stock" but since "a majority of teams" could purchase the slide components from http://www.adafruit.com/ then you should be fine under R04. A real "nitpicky" inspector might argue that you all have bought an assembly rather than just a COST part though so it might be best to ask on the FTC Q&A and link the adafruit website not the ebay one.

[cadandcookies]

I would definitely ask via Q&A on this part. I'd personally pass it, as long as you had proper supporting documents to convince me it was a COTS part (it looks like a part comparable to other COTS linear slides), but there are others in this thread that disagree with me, and I certainly won't be at your event. Also I would recommend reading through the robot manual again, specifically R04 about COTS parts.

Outside of that, this seller looks reputable, but it's generally better to find things at actual company websites-- you have no guarantee that you'll be able to order replacement parts from an ebay store if something breaks, while McMaster is unlikely to disappear overnight.

[ehochstein]

I would suggest taking a look at the MakerSlide. I haven't personally used it but I've heard very good things. Also, it was already ruled legal in the Q&A.

https://www.inventables.com/technologies/makerslide