Description
The Diamond Series has been a go-to YHM forearm for years, and this rifle-length version keeps everything that made it popular. The instantly recognizable diamond-shaped cutouts aren't just for looks. They help vent barrel heat and trim a little weight while giving the rail a distinct profile you can spot across the range. Underneath the style is a genuine free-float design, meaning the handguard clamps to its own barrel nut instead of touching the barrel, so you can lean on it, add a bipod, or push against a barricade without pulling your point of impact around.
What Sets the YHM Diamond Series Rifle Rail Apart
You get full Picatinny real estate at the 12, 3, 6, and 9 o'clock positions, so mounting flip-up sights, a light, a laser, or a vertical grip is straightforward. The top rail runs extended and sits gap-free against your upper receiver rail, which matters when you're running a rear sight up top and want it to line up cleanly with a front sight or optic. Every rail slot is T-marked, so once you note where an accessory lives you can pull it and put it right back in the same spot.
Build Quality on the Diamond Series Forearm
The forearm tube and barrel nut are machined from 6061-T6 aluminum and hardcoat anodized matte black to military spec. The jam nut and anti-rotation screws are steel with a matching matte black plating, and that anti-rotation hardware is what keeps the whole assembly from working loose over time, which is a common gripe with cheaper clamp-on rails. Overall length lands right around 12.58 inches with an inner diameter of 1.75 inches.
Worth knowing before you order: this is a round-tube quad rail, so with rail panels installed it runs a bit chunkier in the hand than a slim M-LOK tube. Plenty of folks like that fuller grip, but if you've got smaller hands it's something to keep in mind. Installation is manageable for anyone comfortable with a barrel nut swap, though a proper YHM forearm wrench makes it a whole lot easier.
Key Specifications
- Manufacturer: Yankee Hill Machine
- Manufacturer Part Number: YHM-9635-DX
- Model: Black Diamond Series
- UPC: 816701012613
- Product Type: Handguard / Forearm
- Rail Style: Quad Rail Picatinny
- Length: Rifle Length (approx. 12.58 in)
- Inner Diameter: 1.75 in
- Mount Type: Free Float
- Material: 6061-T6 Aluminum
- Finish: Hardcoat Anodized Matte Black (Mil-Spec)
- Hardware: Steel Jam Nut & Anti-Rotation Screws, Matte Black
- Platform: AR-15
- Color: Black
- Made in USA: Yes
What’s Included
- Rifle-length Black Diamond Series handguard tube
- Barrel nut (YHM-9483)
- Jam nut
- Anti-rotation screws (2)
- Installation instructions
Frequently Asked Questions
Will the YHM Diamond Series rifle-length handguard fit my AR-15?
It fits most mil-spec AR-15 pattern rifles and comes with its own barrel nut and mounting hardware. It will not work on rifles that use a delta ring and handguard cap setup, since it's a free-float design. Check your upper receiver against mil-spec dimensions before ordering to be safe.
Do I need special tools to install the Diamond Series forearm?
You'll want a proper armorer's wrench, ideally the YHM forearm wrench made for this rail, plus a vise block and a torque wrench for the barrel nut. The install is a standard barrel nut swap that most folks comfortable working on an AR can handle at home. If you'd rather not tackle it yourself, any gunsmith can knock it out quickly.
Is this a true free-float handguard?
Yes. The Diamond Series clamps to its own dedicated barrel nut and doesn't contact the barrel, so pressure on the forearm from a bipod, sling, or barricade won't shift your point of impact. The anti-rotation screws help keep everything locked in place over the long haul.
What can I mount on the Diamond Series rifle rail?
It offers full Picatinny rail at the 12, 3, 6, and 9 o'clock positions, so you can run flip-up sights, weapon lights, lasers, vertical or angled grips, and bipods. The extended top rail sits flush with your receiver rail for clean sight alignment, and the T-marked slots let you return accessories to the exact same spot every time.





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