These replace the short, low rails that come with the stock Tri-Rail PS90. These have more slots - and they also allow you to use accessories with a wide optic such as an Eotech (if you mount an EOtech on a PS90 tri-rail, you can't get accessories on and off on the side rails)
Attachment screws are included.
The pair is available for $25 shipped (I am in Texas)!
Please e-mail me at: goldfishpanda@hotmail.com