Fits up to 300mm outer diameter.  I.D= 300mm
One of the biggest masks I make.

Tri-Bahtinov Focus Mask for Telescope - Dobson 10 Inch or any 12.75 Inch External diameter telescope. most 10 Inch Meades. External  SLIDE ON fit like cap. Condition is New. Shipped with USPS First Class. Software Designed and tested. Works great with these and similar models. 3d printed and designed by Spencer 3d. As always fast free USPS SHIPPING. 2 TO 3 DAY SHIPPING. BLACK,  If need in different color let me know or if need one to fit your telescope let me know I may already have a design, if bot I can design to fit yours. May fit others same size or other brands.

SHIPPING CHARGES WILL BE CHANGING AND MOST ITEMS THAT WERE FREE SHIPPING WILL SLOWLY START TO CHANGE OVER TO SHIPPING THAT IS CHARGED TO THE BUYER. THAT IS DUE TO INCREASE PRICES OF SHIPPING SUPPLIES AND SHIPPING CHARGES. ME PAYING FOR ALL THAT IS TOO MUCH AND REALLY HURT THE BUSNESS LAST YEAR. BUT WITH ADDED SHIPPING CHARGES WILLK BRING LOWER ITEM PRICES. AND FASTER AND BETTER SHIPPING OPTIONS.