24.3mm is not at standard size, you have 3 options for an MTB, 25.4mm (older, now uncommon on anything but low end) 31.8mm pretty much current industry-standard & 35mm (new-ish standard, struggling to gain ground) for almost everything on a modern bike metric is used for measurement

If your changing stem, you will need to match the handlebars, as TimothyH notes; given the age of the bike (well over 10 years as it has a 25.4mm stem) you may find getting matching length stem to your current one hard to find (or very easy if on clearance)

If you take the bike off-road, you may want to look at going shorter than the original stem, as generally, bikes will ride better off-road with short stems than were used in the past.

Have a look here at a post with shows this Accidental build: Orange Evo2 | Retrobike