Amazon.com : Astromania Bahtinov Mask Focusing Mask for Telescopes - FM120mm for a Tube Outer Diameter (OD) from 125mm-180mm - can be Mounted with The Brass Screws Inside or Outside The drawtube :
Amazon.com : Astromania Bahtinov Mask Focusing Mask for Telescopes - FM60mm for a Tube Outer Diameter (OD) from 65mm-100mm - can be Mounted with The Brass Screws Inside or Outside The drawtube :
Farpoint Adjustable Tri-Bahtinov Mask - 11 Inch to 14 Inch OTAs – FarpointAstro
Amazon.com : Astromania Bahtinov Mask Focusing Mask for Telescopes - FM180mm for a Tube Outer Diameter (OD) from 195mm-240mm - can be Mounted with The Brass Screws Inside or Outside The drawtube :
High Precision Tri-Bahtinov Focus Tool – Johannes Scientific
Farpoint Snap-In 72mm Camera Filter Bahtinov Focus Mask FP442
Bahtinov mask - Wikipedia
Bahtinov Masks
Astrozap Focusing cap with built-in Bahtinov focusing mask for 80mm refractors and similar scopes | Astronomics.com
Bahtinov Focusing Mask 100x100mm fits Cokin Z Series - Etsy
How to Use a Bahtinov Mask | Easiest Way Focus Your Telescope