... Series 4000 filters thread into the barrels of virtually all 1.25" eyepiece brands. Meade Series 4000 filters are a large 26mm in clear aperture and are manufactured from the purest crown optical glass, dyed-in-the-mass ( not "color coated"); there are no finer filters available for telescopic applications. ... For visual applications Series 4000 filters thread into the barrels of all Meade 1.25" eyepieces, and into the barrels of virtually all other 1.25" eyepiece brands as well. ... Meade 4M | ...