"F" Marked - Front Sight Base - (A Frame, FSB)

(4 reviews) Write a Review
$39.00 - $110.00

 Standard Finished (Unaltered) .625 and .750 without Sling Swivel Assembly are the only items offered at a discount.


** "Non-F" marked - (Here)


Standard Milspec Front Sight Base (FSB or A-Frame) for all "Flat Top" model USGI Colt M16 / M4 models. Virgin part with no holes drilled.


To get the right version, you first need to decide which Gas Block size you need (.625 or .750):

- .625 is for "Pencil" profile barrels, measured as .625 inches in diameter at the Gas Block location on your barrel (diameter of barrel at the gas hole location)

- .750 is the size used on most barrels today (since 1984 or so). Standard M16A2 / M4 profile size.


Second, choose which height you need:

- Non-F marked is for all carry handle models (AR15, M16, M16A1, M16A2, XM177, Commando, etc.)

- F Marked is for flat tops - The page you are looking at now


Next, choose if you need the Bayonet Lug shaved off or not.

- Colt shaved the Bayonete Lug off all models with Barrels too short to attach a Bayonet (607,  XM177, XM177E1, XM177E2, GAU-5, 605, early Commando models, etc.). This was the Rule up to about the 1990's - when this practice was stopped and everything came with a Bayonet Lug whether it could use a Bayonet or not.

- All Rifle models (except 605) had a Bayonet lug; as do Carbines with Barrels long enough to attach a Bayonet.


There are 2 different styles of "Shaved Bayonet Lug":

- Our standard method, as shown in our pictures, is to remove the Lug completely. If ordered online, this is what we will deliver to you.

- The second method is to shave off only the wings of the Lug, leaving a center post still in place. This serves to make the Bayonet Lug inoperable, yet still look like it is there. For this option you would need to ask for it in the "Comments" section at Check-Out.


* Notes on Remove Flashing:

All AR15 / M16 models up to about the mid-1960's had the Flashing removed on the FSB.  Back then this was considered a cosmetic necessity. As the Vietnam War picked up this extra manufacturing step was deleted. This is still the case today and most of Us have grown up thinking the Flashing was always there on our FSB.

Due to the fact removing this Flashing is labor intensive and most Folks don't even realize this was done - we offer it as an Option.



  • Steel
  • Made in USA
  • Limited Lifetime Guarantee
  • Does not come with Front sight post, spring, or detent. For the M16A1 or the M16A2/M4 go here.
  • Modifications will need to be made in order to fit with original colt handguard cap with the "lip".
  • 5
    Front sight base

    Posted by Richerd McGough on 21st Sep 2020

    Nice product,great shipping.I've not installed item,but I see no problems in fitment.

  • 5
    Non F front site base

    Posted by David Schell Sr. on 8th Aug 2020

    Just rite , cant tell the difference between it an a original , super nice folks deal and to talk with . My only problem is I need a Barrel to go with it , hope to get it soon , I think it s worth the wait .

  • 5
    Front Sight Base

    Posted by John Cashwell on 8th Jun 2020

    Perfect fit for my Colt SMG Clone Build

  • 5
    A2 Front Sight Base

    Posted by D.J. Davis on 27th May 2020

    Great quality. I ordered the "Standard Finish" FSB. It is very nicely finished with smooth flashing. Just as pictured, the entire FSB body is parkerized including the barrel journal surface. Well worth the price for the quality of workmanship.