Is there any difference in cog spacing between road and mtb cassettes? I am sure there isn't, but once i thought i read that you couldn't use brifters with a mtb cassette, so that made me wonder if the spacing is different.
'''96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '12 Surly Pacer, All are 3x8,9 or 10. It is hilly around here!
No, Shimano road and MTB cassettes are spaced the same if the number of cogs is the same. For example 9-speed road and MTB cassettes are spaced the same. Road 10-speed cassettes are unique because there are no 10-speed MTB components.
Giant OCR2, Motobecane Fantom Trail, Specialized Hard Rock, Giant Nutra
They're the same. "Mountain" cassettes work fine with brifters. If you exceed 30 teeth on the largest sprocket though you will need to change your "road" rear derailer to a "mountain" rear derailer which will work fine with brifters. OTOH, front derailers and shifters a for road and mountain require a different amount of cable pull and are not interchangeable.