The Fin Flange Flip-Flop

Humor yourself for a moment and read this out loud really fast: nail fin; flush fin; mounting flange; frontal flange; face flange; frontal fin; non-frontal flange; mounting fin; exterior flush fin; surface flange.

So far, our industry has come up with these 10 terms (and a few others) to describe a grand total of two window frame appendages. I’m actually kind of amused by this and I’m not faulting the industry, but we’ve stirred up some confusion for ourselves. This affects understanding of product, installation technique, and selection of installation instruction documents. For instance, we don’t want an installer driving screws through a “flush fin,” as that could virtually ruin the window (more on that later).

The terminology seems to differ among manufacturers, dealers, industry documents, and especially regions of the country. Some sources are adamant about the term they use. They will probably never change and really don’t need to. However, let’s define the apple from the orange to get on the same page. I don’t expect to convince everyone to use the same terminology, let’s just please, please stop creating any more new terms for each.


Let me start the separation by saying that “flange” and “fin” can be, and frequently are, interchanged. The adjective in front of “flange” or “fin” is the key. For the major breakdown, I will use “flange” and the broadest adjective for each.

There are two primary types: a “mounting flange” and a “frontal flange.” They each have a different location on the product frame, as well as a different purpose. Simply described, a “mounting flange” (about 1 1/2-inches wide) is typically set back about an inch or so from the frame face exterior. As the name implies, fasteners will be installed through this flange to mount the product to the wall structure. The flange is usually pre-punched to receive fasteners. Exterior casing or the exterior veneer ultimately covers this flange.

A “frontal flange,” on the other hand, is flush with the frame face exterior. Note this is not an anchoring feature, and will not be penetrated by fasteners. Its purpose is only to trim out and/or help seal the exterior. Two primary versions are available: a narrow width (about 5/8 of an inch or so) sometimes referred to as a “Florida flange;” and a “flush fin,” which has a wider width (about 1 3/4 of an inch, or so). In either version, the “frontal flange” window is typically anchored through the jambs or with mounting brackets.


A mounting flange product is typically used with a membrane drainage wall system, with nearly any veneer, throughout most of the country. The flange helps enable integration with the building wrap and flashing, although should not be considered flashing by itself.

Narrow frontal flange products are commonly used for surface barrier wall systems with wood bucks such as, but not limited to, FMA/ AAMA 200-12 “Standard Practice for the Installation of Windows with Frontal Flanges for Surface Barrier Masonry Construction for Extreme Wind/Water Conditions,” thus the catch name “Florida flange.” In some cases, a wider frontal flange would be applicable if 2x wood bucks were used.

More common for the wider frontal flange products is a replacement product in the drier southwestern regions of the country. AAMA 2410- 13 “Standard Practice for Installation of Windows with an Exterior Flush Fin Over an Existing Window Frame” is the most common application. This replacement technique prevents disturbance of the membrane integration because the original window frame is left in place. You would be installing this frontal flange (“flush fin”) product over an existing mounting flange frame.


Either type of flange can be “integral” or “non-integral.” Integral means the flange is usually extruded as one piece with the frame and continuous around the entire perimeter (including the corners).

Non-integral, sometimes called “applied,” is typically pressed or snapped in to an accessory groove of the frame—it is optional. This makes one window product more versatile, giving it a finless (or box frame) option. However, in the case of an applied mounting flange, these more flexible flanges usually require some supplemental anchoring through the jamb. Given this variety of terminology, if nothing else, just remember, “One is set back to tack, the other is out front to finish.”

Jim Snyder is an AAMA-certified FenestrationMaster and InstallationMaster who shares his years of installation field experience as an industry writer, speaker, trainer and project/product consultant for dealers and manufacturers. A member of various industry organizations, Snyder also is involved in instructional document creation and revision. Contact him at