yes

Yes, the standard Spike’s Tactical lower receivers (often referred to as ST-15, Spider, or M4 LE) are manufactured to MIL-SPEC (Military Specification) dimensions. They are forged from 7075-T6 aluminum, feature a "low shelf" for RDIAS (Registered Drop-In Auto Sear) compatibility, and use standard MIL-SPEC fire control groups.
Regarding the Rare Breed FRT (Forced Reset Trigger) product:
Fit: Because the Spike's Tactical lower is built to true MIL-SPEC standards, it is physically compatible with the Rare Breed FRT-15, as the trigger requires standard AR-15 trigger pin locations and internal dimensions.
Function: Users have reported successful installation and function of the Rare Breed FRT in Spike’s Tactical lowers.

Yes, absolutely.

Why yes the Spikes Tactical Mk4 is a milspec lower receiver. It is made from 7075-T6 aluminum forgings. Buttstock, milspec buffer tube and buffer tube.

Good morning to you!! Yes the Spikes Tactical Mk4 is milspec and will hold the rare breed reset product. Hope this helps. Have a good rest of your day.
🇺🇸🇺🇸 'Merica' 🇺🇸🇺🇸

Yes, Spike’s Tactical lowers (including those featured on their M4 LE and various builder sets) are built to MIL-SPEC standards. They are forged from 7075-T6 aluminum, feature a Type III Hardcoat Anodized finish, and typically use a "low shelf" design, which makes them generally compatible with aftermarket, drop-in trigger systems, including those requiring more space like the Rare Breed FRT-15.

Hi Leon, yes, the Spike Tactical MK4 is considered to meet or exceed mil-spec standards. It is made with materials and finishes that align with military specifications. The Spikes Tactical MK4 lower can accept a Rare Breed trigger.
Stay safe & have a great day!

Hi Leon and welcome. Yes Sir it is a quality "Forged" Lower and will hold the Rare Breed reset product without issue. This complete lower receiver assembly is meticulously crafted from a 7075-T6 aluminum forging for maximum durability. It features a generous mil-spec type III class 2 hard coat anodized finish, providing incredible protection against the elements and heavy use. This unit comes fully equipped with the Spikes Tactical Pro Pistol Grip, a standard M4 carbine collapsible stock, and a reliable 6-position mil-spec buffer tube. Cheers, stay safe and enjoy!