The .22 caliber PelletgageR has 48 precision apertures, and is the fastest way to sort out the exact head diameter needed. It is offered in six sizes, 5.50, 5.51, 5.52, 5.53, 5.54, and 5.55 mm. (Some sizes are Special Order) You may wish to order two aperture diameters, so that you can sort using a "go/no-go" approach. For instance, if you want 5.51 mm pellets, get a 5.50 and a 5.52, and you can sort to have pellets < 5.52 and >5.50 mm.