I have several refractors. My 4" and 6" Clarks came with Herschel wedges, which I use frequently. I made an adapter to use them on my 3" refractor and another 4" refractor, no problem. I also have a 1.25" Bausch & Lomb Herschel Wedge, which I use on all the above scopes. But my other refractors are 8" F13. Looking around, I see the available Herschel Wedges are for use up to 2500MM Focal length. The 8" refractors are 2641MM. I realize it is only 141MM longer (5.6") but I figure the manufacturers put the max there for a reason. I am hesitant to try my current Herschel wedges on my longer Focal length scopes, obviously I don't want to crack the prisms. Would they be safe? What about the new ones that say 2500?
By the way, I have been using my Clark wedges for many years, for hours at a time with no problems. I have taken the scopes to public observing places and they have been trained on the sun all day with no problems, so I know they hold up under long term use.
I do have a couple other solar accessories for the 8" scopes, but would like to have wedges on both at the same time.
The first picture is one of the Clark Herschel wedges, the second a Dawes type solar eyepiece (two rotating rings, the bottom with graduated size holes, the top with graduated density filters), the last a polarizing solar eyepiece.