When you go to buy new tubes or wheels for your vintage or antique vehicle, there’s a good chance you’ll be asked about valve stem offset.

Valve stem offset is a vital spec to know and if you order the wrong valve stem style for your wheels, then there’s a good chance you won’t be able to fit them properly inside the rim.

The good news is, valve stem offset is pretty easy to understand, and to prove it, the fine folks at Coker Tire made this short video. In just under a minute you’ll get a pretty straightforward demonstration of what valve stem offset is, and how it’ll impact your tire tube purchase—and perhaps even your wheel choice.

If you’ve got an antique car or truck running tube tires, it’s worth checking out: