Razors FSK Ratchet Buckle black
Sold as set of 2
These type of buckles or straps all have only one hole on both sides. They only vary in length. As long as the length will work, you can use any brand buckle on any brand boot.
Buckles that are mounted like this are called SBM2 which stands for Standard Buckle Mount with a total of 2 bolts.