Available in 4.51mm, 4.52mm, for .177 and in 5.51mm, 5.52mm for .22. These precision reamed brass sizers help ensure that every pellet you load into your air rifle is exactly the same as the last one, reducing group size and eliminating Flyers in the field. Please note: These sizers are intended to reduce the pellet diameter to a preset size. They cannot increase the pellet size.