There are several posts about Williams Fire Sights on Rem870.com:
–Williams Gun Sight Company: Remington 870 Universal Ghost Ring Firesights
–Williams Gun Sight Company: Remington 870 Fiber Optic ACE IN THE HOLE Sight Review
–Remington Ghost Ring Firesight Set by Williams Gun Sight Company, Inc.
I decided to try another type of Williams Fire Sights on my Remington 870 with rifle sights: