These guides will work in your atc350x, trx350d, atc 250sx, atc250es big red, trx300 utility, trx 300ex, trx 250x, and various other models.
These are NOT oversized guides that will require extensive head machining, these are stock replacements for your worn or cracked guides. However, they will need honed/polished to fit after interface fit installation
We also have bronze guides available for the folks wanting all the performance they can get