Variable Filter System (VFS) with a 1.25" barrel size and carrying case. Frankly, I found this filter isn't very useful in my apo refractor or premium newt (which already have great low-contrast detail) and requires a barlow for focus since it requires additional in-travel in your focuser.
The glowing review on the Sirius Optics site was for a large achromatic refractor. Indeed, I tried this filter on a 9" achromatic refractor at a local observatory and it was a marked improvement with lots of detail displayed for Jupiter that was not seen without it. I suppose this filter works best as a minus-violet filter on steroids for achromats.
The filter focuses without a barlow in most SCTs.
$140 shipped insured via FedEx ground to CONUS. Money order, bank check, or PayPal accepted.