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Ultra Spacing
An early type of 6-speed freewheel made by Sun Tour, in which the sprockets were closer together than those of a 5-speed or normal 6-speed freewheel., allowing the use of a 6-speed freewheel on a hub built for a 5-speed cluster, in a frame with 5-speed (120 mm) dropout spacing. A 7-speed freewheel could be used with 126 mm dropout spacing.
Ultra spacing, 5 mm center to center,is identical with the spacing of Shimano 7-speed cassettes; Shimano 7-speed or 8-speed shifters can be used to index these freewheels. This shifting isn't as clean as with Hyperglide cassettes, but it is much nicer than friction shifting.
Ultra spacing was made possible by the development of chains in which the ends of the rivets did not protrude far past the side plates. 7- and 8-speed freewheels are also Ultra spaced, but the term is mainly used to describe the narrow 6-speed units.
