What size piston is this?

The piston is .50 mm bigger than the original bore and stock piston.I believe you have a 96 200(with a plated cylinder) which cannot be bored unless the cylinder has been sleeved.
If the cylinder is plated still and within spec you will have to order a new piston A,B,C or D and rings for the bike, unfortunatly you cannot use the ones you have now.
If the engine has been sleeved then you can take it to a shop and have it bored,but if its on the original bore size you have 1 piston between the stock size and the .50,so you might still want to go with the .25 and keep the .50 for the future.

Hertz...and not exactly.....

Check the part number on the Pro-x website. What you have is NOT an a/b/c/d piston.

Try to stick it in a 'std' 200 and you'll have to use a very big hammer! ;)

re: bores, plates and stuff.

Plated cylinders can certainly be bored. Then they are replated. USChrome, Langcourt are just a couple that do this.

FRP will do it. EG (forward motion) will do it.

I'M doing it to my damaged cylinder.

You can get it bored to whatever you wish. EGs 225 kit consists of a bore and replate (with a wiseco piston).

The rings are all the same......the piston alpha desigation is only about 1/2 a thou..so it's not a great big deal. Still, the better the fit, the better.

Clear as mud?

Ask summore...and keep asking until you get the right answer (don't know how you'll figger THAT out.....;) )

Check HERE for a pro-x size chart.

..edit..
It's attached to post#12

Sorry Nm_KDX200 and Canyncarvr I thought Nm was trying to do a basic top end,put in a new piston,rings etc.and had bought the piston for a stock bore size replacement.You are correct the cylinder can be bored out and replated for the oversized piston without installing a sleeve.
Boring and replating with the Pro-X piston you now have(.50) would give you a new engine size of 201.704 cc's.