I gotta be honest, I had this piston on my shelf and I cannot remember the specs on it. I used to have a 250r with a DR 265 hyperdyne cylinder on it. Goodness that thing was fast, but I sold it a long time ago. I think this was a spare piston I had for that kit. The piston is slightly used but I can tell it was not run much. The top of the piston is clean. There is a small dent on the intake side at the top edge of the piston. It doesnt look bad. It almost looks like the piston may have been dropped or something. Although I don't recall doing this. You may can see this in the pic but my pics aren't that great I can try to get better ones upon request. Also if any measurements are needed from this I can get those upon request. The top of the box says hyperdyne 685. There are no numbers on the top of the piston. Maybe you can tell from the pics if this will work for your application.

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Here are some better pics. Those earlier ones are too blurry and its hard to see any marks on the piston. I also pointed out the small dent in the edge. Also the piston rings and circlips are included. Again, not sure on any details of this piston. So maybe someone who is familiar with this setup can make sure that this will work.