The Shimano RX100 product line from this era was considered an entry-level racing groupset (so good quality components). We have also confirmed there is no difference between Shimano's RX100 group and it's more popular 105 group...other than the cosmetic finish...and this appears to hold true with these front derailleurs. At one time we offered both models of this vintage in our store (although we have since sold out of the Shimano 105 equivalent model) and they are very similar...other than the polished/silver finish on the seat tube clamp of the RX100 model compared to the enamel (or painted) finish on the 105 model. Otherwise they look identical in design and workmanship.

Our Shimano catalogs indicate the RX100 groupset in the mid 90's was marketed primarily as a eight-speed drivetrain with 130 mm (locknut-to-locknut) spacing. These specs indicate this front derailleur was considered narrow chain compatible, as defined for this period (as the eight speed drivetrain with a 130 mm freehub typically required a narrower chain). Please do keep in mind, however, when we speak of narrower chains from this era, this is relative to the wider chains historically used on regular spaced six speed drivetrains with 126 mm spacing and/or regular spaced five speed drivetrains with 120 mm spacing. Today's nine and ten speed compatible chains are even narrower then those that were typically used on these seven speed drivetrains.

Having said the above, we also compared this model FD-A551 front derailleur to it's predecessor model FD-A550 (the latter of which was marketed in the very early 90's primarily with a seven speed drivetrain). We compared these two units...and specifically the derailleur cages (or chain guides), because we wanted to assess any differences in their width and/or design. After making such comparisons and taking some caliper measurements, it appears this second generation model has a slightly narrower chain guide (especially near the front half of the cage).  As a result, this model FD-A551 should probably be limited to 7/8/9-speed applications, given it's slightly narrower chain guide.  This is not to say this unit would not function on a 5/6-speed drivetrain with a wider chain, but there are better options for such drivetrains (with slightly wider cages) that are still readily available.

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Note to international customers regarding shipping...
We apologize to those that feel some of our international shipping charges are too high. We only charge actual shipping rates, but once an order exceeds a certain amount, we hesitate to use the least expensive US Postal Services First Class International service. We feel this way, because this service is not trackable or insurable...so more risk of loss. We prefer the US Postal Services Priority Mail International service for more expensive orders, because this service is trackable at USPS.com and insurable...so less risk of loss. Unfortunately, this service is more expensive, especially for smaller/lighter packages, relative to the First Class International service. We are sorry about these higher shipping costs, but hopefully our notes help to explain why this is the case.