Are all MTB bars the same diameter?
Thankfully, mountain bike bars come in just one width at the grip: 22.2mm. This means grips are interchangeable with any bar on the market. When it comes to the stem clamp, that is a different story. The most common diameter is still 31.8mm, but older bars can be 25.4mm.
Are all steerer tubes the same size?
Most steerer tubes will be 1 and 1/8th of an inch or 28.6mm some are 1 and 1/4 of an inch or 31.75mm but much rarer. Just measure the inside diameter of your existing stem by taking off the top cap.