This offering is for a new-old-stock Shimano Dura-Ace UniGlide (UG) 7-speed freewheel with a 13-14-15-16-17-18-21 cluster in a nice gray/silver finish. This is a true old stock Shimano 7-speed indexing freewheel with a production window from the mid to late 80's and it's top-end Shimano quality. We are big supporters of vintage Suntour freewheels and have been selling them for years, but these higher-end Shimano freewheels (coming out of Japan) are also really nice and very good quality.  Unfortunately, we do not see very many of the higher-end Shimano freewheels in today's market (and especially in new-old-stock condition).

In terms of compatibility, this is a freewheel, so it will only install on a threaded rear hub (as opposed to the newer cassette/splined freehub designs that are more common today). The threading is British/English, so it's 1.370" x 24 tpi (threads per inch), which was one of the more prominent standards during this period...and very near a couple of other standards. More specifically, there is the Italian standard of 1.378" x 24 tpi with a slightly larger thread diameter and different thread angle, but the same thread pitch as the British/English standard. Then there is the newer ISO standard of 1.375" x 24 tpi (which is the preferred specification of most newer freewheel manufactures) with the same thread pitch and angle as the British/English standard and a thread diameter between the British/English and Italian models. 

When considering the three aforementioned standards, conventional wisdom indicates there is some interchangeability among them...with a few caveats. More specifically the thread pitches are the same, while the thread diameters and angles are close enough that it's possible to install a freewheel spec'd to one standard on a threaded rear hub spec'd to a different standard (among the three included in this discussion). Although, one of the caveats is to avoid switching back and forth between standards, as there is still enough of a diameter and/or angle difference to prematurely wear-out/damage rear hub threading if this (switching back and forth) practice is employed. In other words, it's best to identify a freewheel standard (among the three mentioned) and then consistently use freewheels spec'd to that standard to help preserve the threads on a particular aluminum alloy rear hub. Additionally, we have learned these mix-n-match combinations may not be recommended for stronger riders and tandem applications...where there is additional drivetrain stress...as this combination may also result in premature thread damage to an aluminum alloy rear hub.  I realize this latter commentary is somewhat subjective...and maybe somewhat conservative...but we feel like it's better to error on the downside of product function, so there are no disappointments concerning product performance down the road.