For those of you looking for new genuine Honda/Nissin close match front master cylinders for 350x’s, 200x’s, etc…, the part number from Honda that is current and available is 45510-HM8-B41 for the TRX250. They run about $40.00 from Honda and are a good match for replacements on older bikes.
Recently on ebay I've seen late model master cylinders that are being described as NOS 200X “HB5” or 350X “HA5” and sold for $300.00. They are real Nissin cylinders but are not NOS and not vintage. Here is how to tell the difference between real NOS ones and the newer ones:
The quickest way to tell is on the bottom side. The newer ones have a boss and screw hole provision for the rear brake light controller wire. The original ones do not as there were no 3-wire brake lights on the 200x and 350x, only 2-wire taillights.
Other more subtle ways to tell:
The original 1986 master cylinders use a convex sight glass lens while the new late model ones are basically a flat lens. The exception to this is the HB5-670 part number for the 1987 200x only. This part number used a flat site glass. I attached a photo of an original NOS one I used on my 87 200x restoration.
Replacement master cylinders for the 86-87 200x and 85-86 350x were only sold as complete kits with lever and rubber already attached.
On the 350X only, some the original master cylinders that came on the bikes had “HA5” embossed on the back side. The later replacement ones did not have this marking.
The handlebar clamp on the original master cylinders are concave to accept the countersunk screws, while the late model ones are flat and use 6mm flange bolts.
In the 80’s and 90’s most of the master cylinders sold by Honda came in boxes and not bags like they do today. Also, the labels would have been the older style with the circle.
Hope this helps someone out. The late model ones are great for $40.00. I have one on one of my bikes and its great. Only someone with a trained eye would be able to notice it. I don’t want to see someone fork over $300.00 thinking they are getting the real deal when it is essentially a new part with half the part number conveniently missing by someone using a piece of tape on it and pulling it off. Also, look closely at the photo I posted with the complete part number label and the one from ebay (last photo), the barcodes are an exact match bar for bar as well as the VC and CP numbers on the side. The JD numbers are the lot numbers so they may differ.
People are free to do whatever they wish to try to make money on ebay. I get it, it’s a free market. I’m just pointing these things out and people can draw their own conclusions.