Does this product fit common 2 .in drains? My application requires mating with an existing Sioux Chef 821 clamping ring.

For your application you would need the Pasco Plastic shower drain, ABS (which we carry). You would connect to your drain pipe, loosen the screws, remove the top, then you could add the Schluter Kerdi Drain Residential Kit. This kit is really made for converting standard mud pan shower to schluter drain. usually you do this when the drain is already poured in concrete and you can not cut off and glue new one in. Please give us a call and we can talk about your project. 1-800-938-7925