The Ultimate Guide to the Surefire M951 Weaponlight: Part III
This article is the third part in a comprehensive overview of the Surefire M951 Weaponlight. If you haven’t read the overview of the M951’s parts designations and the M951 generation guide, you can check that out here: Part II
Comprehensive List of Changes to M951 Parts by Generation
With what I have seen from pictures and my own lights, there are numerous possibilities for legitimate factory configurations for M951s. There are definitely and assuredly exceptions to the parts list. That being said, exceptions prove rules, and the following is a list of what I consider the rules for the individual parts that make up any given Surefire M951.
All M951s are anodized gray, but the shade of gray varies wildly, although with some consistency. My personal lights and parts have ranged from being super cool baby blue gray, to cool gray, to just gray, to black gray, to light gray, to warm gray, to tan brown gray. I personally see a correlation with cooler grays to older lights and warmer gray to newer lights, but I accept that there may be exceptions to that rule, given the parts that I have seen and personally owned.
FM63 Removeable IR Filter
The FM63 Removeable IR Filter is an M951 accessory included in the M951 KIT02 package. It filters the light from a P60 Lamp to night vision safe levels. As far as I can tell, there are no differences between any of the filters between generations.
The Generation 1 and 2 bezel, according to all the pictures I have found, are the same. It is perfectly cylindrical with two fins toward the rear, presumably for heat sinking the P60 Lamp, with a hex shape at the thread mouth for removal of the bezel with a wrench.
The Generation 3 bezel is different in that it has very shallow fin shaped flats cut into it, giving it an almost angular appearance, and the cooling fins have been removed, leaving a giant gap. The hex shape at the thread mouth is the same.
The M2 Bezel is also referred to as a “shock isolated” bezel, as it’s construction mitigates the recoil impulse that the fragile P60 Lamp would otherwise feel from being in a light mounted to a weapon.
The P60 Lamp is the consistent factory lamp assembly for all variants of the M951. It is an incandescent bulb as opposed to a more modern LED. There are other Surefire factory lamp assemblies, but the P60 is the bulb found inside most, if not all stock lights and light kits out there.
The Generation 1 collar, as far as I can tell with the few pictures I have, is a round collar with fine line serrations for hand removal.
The Generation 2 collar has a hex band around it for removal with a wrench. It also has two notches on the body end and two double width notches on the bezel end for removal with a flat head screwdriver. I read somewhere in passing that at one point, these notches weren’t present, but I cannot verify this.
The Generation 3 collar has a star band for, presumably, easier hand removal of the collar, and 4 double width notches on the bezel end that are deeper than on the Generation 2. The Generation 2.5 lights are generally just Generation 3 lights with one of the major differences being the use of the Generation 2 collar instead of the Generation 3 version.
The MH90 Body, regardless of generation, tends to feature a six digit serial number with a letter prefix, usually the letter “A”. I remember reading somewhere in passing that serial numbers and the letter prefix had some deeper significance, but that source has since been lost to the internet.
The Generation 1 body is by far the thickest and most unrefined. It is wide and rounded out with a flat where the Surefire name is laser engraved. I have seen the Generation 1 body referred to as the “Fat Body” but that nickname is much more commonly used to described the Generation 2 body.
The Generation 2 body is more trim than the Generation 1. It is known as the “Fat Body” due to it’s juxtaposition with the even more trim Generation 3 body. The body is rounded out with a gap between the body and mount on the bottom, more narrow in the center, and wider where the mounting points are.
The Generation 3 body is a narrower version of the Generation 2 body. It is substantially more narrow than the Generation 2 which saves a little weight. Being the final and largest produced variant, there are a few different sizes, formats and fonts for the Generation 3 body laser engraving.
There are some other nuances worth noting with regard to the Generation 3 body. There are two different laser engraving font styles that I have seen, one smaller like on the Generation 2, and one larger.Additionally, at some point, the screw holes on the body for the M49 Thumb Screw Mount were switched, moving the thumb screw position from the left side to the right side (relative to the bezel facing away from the user). The picture below demonstrates a Generation 2 body with left facing screws, and a Generation 3 body with right facing screws. I have seen Generation 2.5 lights with left facing screw bodies, and consider this one of the oddities of Generation 2.5.M49 Thumb Screw Mount
The Generation 1 mount cinches down onto an M1913 rail by way of two solid screws which are serrated on the rim for hand tightening and removal, and have flat head slots for cinching down and loosening with a screwdriver. The Generation 1 mount is always bolted on the right side of the light body with 3 hex head screws, with the thumb screws always appearing on the left side of the body. The thumb screws also bolt clean through the other side of the mount, sticking out slightly when fully tightened.
The Generation 2 mount is attached to the body with 2 hex head screws instead of 3. The thumb screws themselves are longer than the Generation 1, and are hollowed out instead of being solid, but are still serrated on the sides for hand mounting, and slotted for flat head screwdriver mounting. The threaded portion of the thumb screws are also captive inside of a flush fit tube in the mount, and do not bolt all the way through anymore. The bolt on side of the mount is squared off, while the clamping side is more angular.
The Generation 3 mount is similar to the Generation 2, but with some small changes. The body attachment screws were replaced with Torx screws, and the thumb screws are much more shallow than the Generation 2, but still have the same hollow makeup, serrations, and screwdriver slot. Both the bolting and clamping side of the mount are now angular as well.
Additionally, there is a transitional or Generation 2.5 M49 Thumb Screw Mount, which has Generation 2 style thumb screws, and a Generation 3 style angular bolt on side.XM Tailcap
The Generation 1 M951 did not come with an XM Tailcap from what I can find.They instead used the early UU07 Tailcap, which features a permanently installed 7 inch Generation 1 tape switch and no other means of activating the light. I have also seen this tailcap on early Generation 2 lights.The Generation 2 M951s were the first ones to feature the XM Tailcap, which would become the standard tailcap for Millenium Series lights. During the production of the M951, the XM Tailcap stayed mostly the same. The only differences between Generation 2 and Generation 3 XM Tailcaps are the finish on the ribbed thread ring and the tape switch port. The Generation 2 colors range from bright silver, to cool gray, to warm gray, all of which are aluminum. The latter 2 colors are almost assuredly in line with the wide variation in Surefire’s Gray finish, and are probably an indicator of age as well. The Generation 3 XM Tailcap is the exact same design as the Generation 2, but the ribbed thread ring and tape switch port are composed of black plastic.
The XM Tailcap has a few key features which make it a marked upgrade from the Generation 1 UU style tailcap. The XM has a click switch to toggle the light on and off, and a port for installing and replacing removable XT Tape Switches. The tape switch port also has an attached plug to fill the port when a tape switch is not being used. Moreover, the click button and tape switch combo also provides activation redundancy, allowing for modular and ergonomic momentary tape switch activation, and for reliable and consistent constant on button activation in case the tape switch is unplugged, damaged or otherwise compromised. Lastly, the XM Tailcap has what Surefire calls a “system disable” feature, which to my knowledge is just un-threading the tailcap to keep it from actuating.
XT07 Tape Switch
The different generation XT07 Tape Switches are all very similar and function the same way, providing momentary only activation of the M951.
Generation 1 tape switch features an exposed metal plug, a rubberized cable, and a pressure pad covered in a thin synthetic layer, possibly neoprene.
The Generation 2 is the same as the Generation 1, but features a refined pressure pad with a rubber cover that is much more sturdy than the Generation 1 version. It also features Surefire’s logo.
The Generation 3 is the same as the Generation 2, but the exposed metal plug has been rubberized at the grip point for added protection and ease of removal.
Phew, alright. Thus ends the breakdown of all the M951 parts by generation. The next section will cover upgrades and accessories for the M951, both factory and aftermarket.
If, after reading this saga, you’ve bought a stock or beater M951 off eBay, from a local surplus store, or from a crafty veteran who pilfered a box or two of them after being discharged, and would like to know what upgrades you can add to it, check out Part IV.