Inner tubes
 

why does my my back innertube say 700 and my front one says 27

they can be interchangeable. those two numbers refer to their diameter. there should be other numbers specifying a width

I have some that say both! :thumb:

27" and 700c are "close enough" for tubes, but not for tires.

700C, sometimes AKA 28” has a 622 mm bead seat diameter.
27”, not to be confused with 27.5” has a BSD of 630 mm.
If the width is OK, the tubes are interchangeable.
There’s another 28-something” with a 635 mm BSD.
Those are usually wider, so not compatible with the majority of road bike sized tires. But might interchange with 29er and hybrid tires.