FS2000 hammers are a little beefier than PS90 hammers. This hammer is compatible with all FN bullpup trigger packs. Aside from being beefier this hammer is also made of slightly harder plastic than PS90 hammers. Though practically imperceptible, the harder plastic does offer less friction than the PS90 hammers. If you buy this hammer and a PS90 trigger pack, we can install the hammer in the pack free of charge. This hammer can be used in the Delta trigger. Again, the reduction in friction is minuscule, and not worth the extra cost for most customers.