Product Code: 21000

5/16" Hybrid End Mill (Original Router Jig Only)

Current Stock:

Important Update Regarding ATF Regulations and Pro Jig Sales

Due to recent changes in ATF regulations, 5D Tactical can no longer sell or support jigs directly.

Support and Warranty Service: For all Pro Jig customers, will now handle support. Modulus Arms will honor warranty services, provide technical support, and offer replacement tools and parts for all Pro Jig products.

Manufacturing and Sales: While Pro Jigs will continue to be manufactured by 5D Tactical, all sales must now be conducted through our independent dealers to comply with the new regulation. We are no longer permitted to sell jigs or distribute manuals via our website under these new ATF rules.

Legal Challenges: We are actively challenging this government overreach in court. We are optimistic about a favorable ruling from the Supreme Court in 2024, as both the District Court and the 5th Circuit Court of Appeals have ruled decisively in our favor.

Availability through Dealers: In the meantime, our jigs are still available through our dealers, despite our inability to sell them directly.

We appreciate your understanding and continued support during these changes.


Please Note: 5D Tactical AR-15 and AR-308 Router Jigs require the use of our router mill bits. This end mill bit for 80% lower is custom designed and manufactured for 5D Tactical, and is not available for sale elsewhere by any tooling supplier or manufacturer.

What is an endmill?

An end mill is a type of milling cutter, used in machining and CNC manufacturing processes. While at a glance, end mills look similar to common drill bits, they are different from drill bits in their application, geometry, and ability to cut in all directions. Milling aluminum, such as with finishing an 80% lower receiver, is possible with the use of a router end mill cutting tool.

Compact routers have been to this point, the popular choice for enthusiasts who wish to finish 80% lower receivers at home in conjunction with a router based lower receiver jig. This is all for good reason, because they are sufficiently powerful, relatively inexpensive, readily available at home improvement stores, and comfortable to use for extended periods.

Challenges of Milling Aluminum

A drawback for using a compact router to mill aluminum, if there is to be one, is the limiting size of the collet. All compact routers on the market are equipped with a 1/4" collet size. This limits the maximum diameter of the tool, in this case the end milling bit, to 1/4". Since the depth of cut required for milling the FCG pocket of a lower receiver necessitates an end mill length of approximately 4 inches, the result is a tool that is much longer and narrower than would otherwise be ideal for rigidity and strength.

The long length and relative narrow diameter of the aforementioned end mills results in more deflection than what would generally be acceptable in achieving a true high quality finish of the FCG pocket. With other jig designs, the end mill is also unsupported for much of the milling operation, which produces chattering, plowing, and the high potential for tool breakage.

The output of “jolting” or “chattering” the user will commonly feel using other jigs with a 1/4” end mill, is the result of the end mill flexing and bending as it removes material. Not only does the constant unsettling feedback slow the user down, the net effect is a cutting surface that may jump outside of the intended template area. A low quality finish, slow milling operation, and broken end mills are a near guarantee.

Our Answer and Solution

A custom, Patent Pending and industry first 5/16” end mill for use with compact routers. How? The collet area portion of the end mill shank is reduced to a standard 1/4” diameter. However, the remaining length of our end mill, including the cutting surface, is 5/16”. Although the diameter appears slightly larger in physical size, a 5/16” end mill is approximately 4-times stronger than a 1/4” end mill of the same material properties. Additionally, since the 5D Tactical Universal 80% Lower Receiver Jigs orient the router support plate closer to the top plane of the lower receiver than all other jigs, we were able to minimize the length of the end mill. These factors alone result in an end mill which is exponentially stronger than its 1/4” counterparts are, and greatly reduces or eliminates all tool chatter.

We didn’t stop there, our end mill is fully supported at all times by a high speed bearing which is incorporated into our Router Guide Plate. The end mill is supported at all times, in all directions, by a high speed bearing which further reduces and virtually eliminates any opportunity for the end mill to flex. With all factors considered, our Hybrid End Mill will deflect 8-times less than an unsupported 1/4" end mill under the same inputs.

Patent Pending - custom designed 3-Flute 5/16" End Mill. For use with our Original Router Jig Only. 
Router Jig Pro ReadyMILL

Our Patent Pending 5/16" end mill has been thoroughly optimized for milling aluminum 80% lower receivers with a handheld router. The upper portion of the end mill bit for 80% lower, the collet area of the shank, is reduced to 1/4" diameter to allow for use with compact routers which are commonly equipped with a 1/4" collet size. The remaining length of the end mill, including the cutting surface, is 5/16". 5D Tactical is the only jig manufacturer to offer a custom designed, oversized end mill for this purpose.

Through our extensive testing, we determined that the 1/4" diameter end mills offered by other jig manufactures are not optimized for their intended use, leading to slower milling, constant chattering, inconsistent finish quality, and frequent tool breakage. For more in-depth information, please read our 5/16" End Mill Hybrid Analysis which outlines in great detail the performance benefits of our router end mill bits for aluminum design.

Every facet of our end mill bit for 80% lower was considered and refined during an extensive prototyping and testing phase. From the proprietary material makeup, to the design of the cutting surface and flutes, we achieved optimal performance and maximum tool durability. In conjunction with our Universal Router Adapter, the end mill remains supported by a bearing in all directions at all times, further reducing end mill flex and the opportunity for premature tool breakage.