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Old eyepieces pre 1970 usually had 0.965" barrels. Typically small light huygens, plossls, Kellners and orthos up to 25mm focal length.
With better mass maufacturing of lenses emerging at that time bigger/better/wider eyepieces appeared in the late 70's, and the industry standard adopted was 1.25" barrels.
With the advent of the big, heavy ultra-wide designs in the 1980s - Vixen LVW, the first Televue Naglers and Panoptics - barrels had to grow to accommodate the wider fields - hence 2" - and the focusers had to be beefed up substantially to hold the weight of these PLUS a 2" star diagonal.
FWIW 19th century and earlier antique brass telescope typically had unique barrels as there was no standard apart from whatever the maker decided, and for this reason a set of eyepieces was invariably made to match the scope. Lose these and you have a problem, and likewise an antique scope isn't worth much if it lacks the matching eyepiece set.
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