64mm Precise Monitoring prism sealed. These prisms are high quality prisms. They have an M20 x 20 mm standard industry thread. They are manufactured to 2 arc seconds of accuracy.
Softrock have been distributing these prisms for many years, and have found them to be highly reliable. We recommend them highly for monitoring purposes.
See Standard Monitoring prism PSM05.10201
Note that Precise prism is RED cannister, while Standard prism is black.