This adapter allows you to use 1.25" eyepieces in 2" focuser tubes. It is threaded to accept standard 2" filters, so you can use your 1.25" eyepieces with 2" filters.
2" filters screwed onto a 2"-1.25" adapter with 1.25" eyepieces can be very convenient, since you don't need to unscrew and re-screw the filter every time you change eyepieces. However, many shorter 2"-1.25" adapters are usually not long enough to prevent the 1.25" eyepiece barrel from hitting the filter when the eyepiece is inserted into the adapter. Many expensive filters have been scratched and even cracked in this way!
This "High Profile" adapter from Blue Fireball provides the extra clearance needed to ensure that the 1.25" eyepiece barrel will not touch the filter. The adapter is 45mm in length. It provides 15mm of additional clearance compared to their standard low profile adapter; thus it also needs about 15mm of additional in-focus travel.
The adapter also has a brass compression ring that restrains the eyepiece and prevents marring of the eyepiece barrel by the metal set-screw. It weights on 2.4 oz and is a precision machined from black anodized aluminum.Blue Fireball part number: E-08