This image is from an eBay listing, but I'm asking because I found a similar one around our co-op. Seller says it's for a roof rack, but that seems unlikely to me. It's a thick axle (~ 2 cm diameter for the thickest part) with a 100 mm equivalent OLN length with a QR skewer that goes through it. Pretty heavy too - almost a 1/2 pound. I'm thinking maybe it was for an early sealed bearing hub and the bearings pressed tightly onto the thick ends of the axle? But that's just a guess. Anyone know for sure?

Could it be for one of those roof racks where you remove the front wheel and secure the front of the bike by the fork dropouts?

Roof rack makes sense to me. With the wheel off, it works as a dummy axle to clamp into a fork-style rack.

My uneducated guess: adapter for a roof rack or old turbo trainer.

I would say it is an adapter to use a wheel with a through axle into a fork made for a traditional QR. There are 20 mm though axles.

Yes!
Vintage Yakima rack.


Brent

Thanks all!