LBE Unlimited Complete “F”-Marked Front Sight Base Kit — AR-15/M4 | Includes Taper Pins, Sight Post, Detent, Spring, Sling Swivel & Rivet | Model: ARFSB-KIT (ARFSBKIT) | UPC: 706612407830

Restore duty-grade iron sights or build a reliable backup front sight the right way with the LBE Unlimited Complete “F”-Marked Front Sight Base Kit. Purpose-built for modern flat-top AR-15/M4 uppers, this assembly includes the F-marked front sight base, taper pins, front sight post, detent, spring, plus a sling swivel and rivet—everything you need in one, matched package for a clean, professional installation.

Why “F”-Marked Matters

Flat-top receivers sit slightly higher than legacy A2 carry-handle uppers. An “F”-marked front sight base is engineered to the correct height for these uppers, providing proper mechanical zero and worry-free co-witness with popular red dots and BUIS. Translation: your irons line up the way they should—no chasing elevation or running out of adjustment.

Key Features & Benefits

• True “F”-Marked FSB: Proper front-sight height for most flat-top (A3/A4) AR-15/M4 uppers to achieve correct zero with standard rear sights.

• Complete Hardware Kit: Includes taper pins, sight post, detent, spring, and sling swivel with rivet—no hunting for small parts.

• Alloy Steel Construction: Durable, armor-tough build to handle heat, recoil, and round-count abuse.

• Pinned Security: Taper-pin attachment is the gold standard for robust, repeatable alignment on hard-use carbines.

• Sling-Ready: Included front sling swivel and rivet make adding a traditional two-point sling fast and tidy.

• LBE Unlimited Quality: Trusted small-parts supplier known for reliable, mil-style AR components.

Compatibility Note: Most FSBs like this are made for .750" barrel journals (the most common size). Please verify your barrel’s gas block journal diameter and pinned vs. set-screw readiness before purchase.

What’s in the Kit

• LBE Unlimited “F”-Marked Front Sight Base

• 2 × Taper Pins (left-to-right orientation typical)

• Front Sight Post (standard square)

• Detent & Spring (front sight elevation)

• Sling Swivel & Swivel Rivet

Ideal Use Cases

• Flat-Top AR Builds: Ensure correct iron-sight geometry from day one.

• Duty/Defense Carbines: Pinned FSBs resist shift under heavy use and temperature changes.

• Backup for Optic-Equipped Rifles: Maintain a dependable mechanical sighting system that co-witnesses cleanly.

• Retro-Modern Projects: Keep the classic fixed-front silhouette while benefiting from today’s upper heights.

Installation Guidance (High-Level)

For best results, have a qualified gunsmith handle fitting and pinning. Correct installation typically involves:

• Confirming barrel journal diameter and gas port alignment

• Proper FSB indexing to maintain vertical alignment with the receiver

• Reaming/setting taper pins from the correct side for a secure lock-up

• Verifying gas seal and function after assembly

Safety & Compliance: Always follow federal, state, and local laws. Ensure the rifle is unloaded and remove ammunition from the workspace before any work. After installation, perform a safe function check and sight-in.

Performance Advantages You’ll Notice

• Correct Zero Window: Plenty of adjustment travel without bottoming out the post.

• Return-to-Zero Durability: Pinned FSBs hold alignment through heat cycles and physical knocks better than most clamp-on options.

• Consistent Co-Witness: Predictable sight picture with standard rear sights and common optics.

Specs (Typical)

• Type: Front Sight Base, “F”-Marked (AR-15/M4)

• Attachment: Taper-pinned (pins included)

• Front Sight Post: Square, elevation adjustable (post, detent, spring included)

• Sling Interface: Front sling swivel + rivet included

• Material/Finish: Alloy steel with protective finish (manufacturer standard)

• Model: ARFSB-KIT / ARFSBKIT

• UPC: 706612407830

FAQ

Q: Will this fit my barrel?
A: Most users pair this with .750" journal barrels. Verify your barrel’s journal size and whether it’s machined for pinned gas blocks/sight bases.

Q: Do I need special tools?
A: Pinning an FSB typically requires proper jigs/fixtures and reamers. For safety and alignment, we recommend professional installation.

Q: Is the front sight post standard?
A: Yes—standard square post, adjustable for elevation via the included detent and spring using a typical front sight tool.

Q: Will it co-witness with my red dot?
A: On most flat-top uppers, an F-marked FSB provides the correct height for standard co-witness setups when paired with the appropriate rear sight and mount.

Q: Is the sling swivel included?
A: Yes. The kit includes the sling swivel and rivet so you can finish the classic front-sling attachment.

SEO Highlights (What Shoppers Search For)

• LBE Unlimited “F”-Marked Front Sight Base Kit

• ARFSB-KIT / ARFSBKIT complete with taper pins, sight post, detent, spring

• Front sling swivel and rivet included

• AR-15/M4 front sight base for flat-top uppers

• Pinned gas block strength and correct iron-sight height

• UPC 706612407830

Build with confidence and keep your irons true. The LBE Unlimited Complete “F”-Marked Front Sight Base Kit gives you the right height, the right hardware, and the right durability for a dependable AR sighting system—no guesswork required.
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