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The first Dura Ace Hyperglide compatible hub. Was produced to be backwards compatible with UniGlide - note the UG outer threads on the freehub body. The lock nuts are tapered to facilitate installing the 130mm hub in a 126mm spacing frame.
FH-7400 6/7 speed UniGlide (reduced diameter 31.8mm UG thread to allow 12T sprocket, 126mm spaced rear)
FH-7402 8speed UG (reduced diameter UG thread, 130mm spaced rear)
FH-7403 8speed UG standard size UG external thread, full length splines, plus HyperGlide spline and HG internal lockring thread.(130mm spaced rear)
The 7400 series share a unique attachment method. Instead of the normal bolt there is a threaded protrusion built into the freehub, with it's own unique extractor tool.
Also of note, the 7400's hubs started with Uniglide freehubs & then transitioned over to hyperglide.
Replaced Dura Ace Cassette with HG 50 Shimano 105 8 speed 12-25 cassette and a shimano hyperglide compatible chain. All is working, shifting, threading, and feeling nicely solid with no chain skip or weird shifting