It will fit a blade about 4" to about 4 1/4" long (see last photo for example of knife with 4" blade, fully inserted. Knife not included). Up to a 1 3/8" wide guard will be a nice fit. You can then form the sheath to fit your knife.
Custom USA Black Leather Fixed 4 Blade Dagger Knife Boot Belt
Custom USA Brown Leather Fixed 4 Blade Dagger Knife Boot Belt
Custom USA Black Leather Fixed 4 Blade Dagger Knife Boot Belt
Best Boot Knife Dagger D2 Steel with Leather Sheath
Leather Knife Sheath Belt, Genuine Leather Knife Holster Sheath
Timber Wolf Tactical Boot Knife with Clip
Timber Wolf Sitka Blacktail Knife And Sheath
Sheath --- Leather - Econo - (5 inch x 1-3/8 inch Blades
Gil Hibben Bloodwood Edition Alaskan Boot Knife Full Tang Leather
Smith & Wesson HRT Fixed Blade Boot Knife 4.50 Double Edge Blade
CIVIVI Knives Typhoeus Folding Push Dagger Fixed Blade Knife
CIVIVI Knives Typhoeus Folding Push Dagger Fixed Blade Knife
4.5 Inch Blade Sheath