Check the listing for details. Optolyth Spotting Astro 1.25” Ocular Adapter custom machine. Condition: Open box. Listed at 99.00 USD. The original manufacturer’s adapter has not been available for decades. I took a Japanese Antares adapter and had it machined 3 ways to fit the Optolyth large fluorite spotting scopes to accept standard 1.25” diameter oculars. Note 2” oculars won’t focus even without an adapter. Instead of the M 37 x 0.75mm inside ocular hole thread, which is unavailable, this adapter threads onto the outer M 56x1mm male thread on the scope body. Whereas a Baader Clicklock adapter at over $100 is 32mm tall, which precludes standard oculars coming to focus, this adapter is only 15mm tall. You can check your Optolyth by setting both fine and coarse to infinity focus, holding your oculars 15mms above the opening and check for focus at infinity. (The back focus was increased in later 100mm fluorites). I used two machinist’s online quote calculators to estimate what a custom adapter like this would cost from scratch. Answer was about $140 both, about 1 hour professional shop time. Much cheaper to do this mod. A set screw is provided.