Origin of the FMS Profile

The exclusive steel profiles used by Fenestration Metal Smiths in their products have a heritage spanning over 100 years.

The story begins with Sir Henry Bessemer, who in 1856 pioneered a production process for hot-rolled steel, laying the foundation for the manufacture of integrated steel windows and doors.

After World War I, steel windows and doors using the original specialized profiles became prolific in all forms of architecture, both commercial and residential. The minimalist aesthetics of these profiles were in keeping with new fashions, especially the “International Style”, and the demand for light, airy and well-ventilated buildings.

With the advent of these exclusive profiles, manufacturers for the first time were able to make composite windows of almost any size – yet retain such slender lines as to make facades virtually transparent.

The universal profiles in turn gave birth to the “W20” range in 1964 and the “MW40” range in 1992. These modern profiles, and the newly released “MT50” thermal range, are the pedigreed descendants of the original specialized profiles, which FMS uses exclusively for manufacturing its classic steel windows and doors.

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Originally developed to replace single-glazed and puttied-steel windows that were common from the 1890s to the 1960s, W20 can accommodate 1/4” plate glass through 5/8” insulated glass. W20 is an excellent choice for interior doors, separating walls, and specialty exterior doors as well as exterior fenestration that requires a historic look. W20 is accepted by the National Park Service and Department of the Interior for specific steel window replacement on properties listed on the National Register of Historic Places.


  • 1-1/4" profile depth
  • 1-1/8" wide true muntin divider
  • 3/4" wide muntin divider available with putty glazing
  • Lock-in glazing bead with EPDM spline
  • Glazing range 1/4" to 5/8"
  • Two-layer powder coat finish
  • Double weather-stripping
  • Values (5/8” IG):
       - Casement
            - U-Factor: .44
            - SHGC: .22
            - Air/Water/Forced Entry: R-PG35
       - Fixed
            - U-Factor: .33
            - SHGC: .26
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