Holosun 510C Spacer Lower 1/3 Co-Witness Spacer FDE 510CSPACER

Description

This precision-machined aluminum spacer elevates your Holosun 510C to the optimal lower 1/3 co-witness height for improved sight picture and backup iron sight visibility.

Transform your shooting experience by raising your 510C optic to a lower 1/3 co-witness configuration. This spacer provides a clearer field of view compared to absolute co-witness setups, allowing your backup iron sights to sit in the lower third of your optic window rather than blocking the center of your view. The result is faster target acquisition with your red dot while maintaining instant access to iron sights if needed—particularly valuable for AR-15 platforms with fixed front sights.

Key Features

• Precise Height Adjustment: Raises the 510C optic to exactly 1.63 inches (lower 1/3 co-witness height) for optimal sight alignment with standard AR-15 iron sights
• Durable 6061 T6 Aluminum: Aircraft-grade aluminum construction with anodized FDE finish provides corrosion resistance and long-lasting durability
• Streamlined Design: Low-profile construction maintains the sleek appearance of your 510C while adding minimal weight to your setup

Important Compatibility Notes

• FDE Color Matching: The FDE anodizing on this spacer may not perfectly match the exact shade of all Holosun 510C FDE optics due to variations in anodizing batches. The spacer will function perfectly, but there may be slight color differences between the spacer and optic.
• Compatible with all Holosun HS510C and HE510C models (red and green dot versions)
• Not compatible with other Holosun optic models

Why We Carry It

The lower 1/3 co-witness configuration has become the preferred setup among tactical shooters and competitive marksmen for good reason. Originally developed for military applications, this mounting height provides approximately 0.22 inches of additional elevation compared to absolute co-witness mounts, which translates to a less obstructed view through your optic. For shooters who wear ear protection or prefer higher cheek welds, this spacer delivers a more comfortable and natural shooting position. The 510C itself is known for its large viewing window, and this spacer maximizes that advantage by keeping your backup sights visible but out of the way until you need them.

Frequently Asked Questions

What’s the difference between an absolute co-witness and a lower 1/3 co-witness?

Absolute co-witness places your iron sights in the center of your optic’s viewing window, aligned directly with your red dot. Lower 1/3 co-witness raises the optic higher so your iron sights appear in the bottom third of the window. This provides a cleaner sight picture for the red dot while still allowing you to use iron sights by slightly lowering your head position. Lower 1/3 is generally preferred with fixed iron sights, while absolute works well with flip-up backup sights.

Is installation difficult?

Installation is straightforward and takes about 5-10 minutes. Simply remove the four screws holding your 510C to its QD mount, place the spacer between them, and reinstall using the included longer mounting screws. A Torx wrench is typically included. You may need to re-zero your optic after installation due to the height change.

Will this work with magnifiers?

Yes, this spacer is commonly used to align the 510C with magnifiers like the Holosun HM3X. The lower 1/3 height provides better alignment with magnifiers and creates a more comfortable cheek weld when using magnification, especially when wearing hearing protection.

Installation Instructions

1. Ensure your firearm is unloaded and pointed in a safe direction
2. Remove the four mounting screws securing your 510C to the quick-disconnect mount using the appropriate Torx wrench
3. Place the spacer between the 510C body and the QD mount, aligning all mounting holes
4. Insert the included longer mounting screws through the 510C, spacer, and into the QD mount
5. Tighten screws in a cross pattern to approximately 18 inch-pounds (hand-tight with proper tool)
6. Re-zero your optic at your preferred distance to account for the height change

Spec Sheet

• Material: 6061 T6 Aluminum
• Finish: Type III Hard Anodized, Flat Dark Earth (FDE)
• Height: Raises optic to 1.63″ (lower 1/3 co-witness)
• Compatibility: Holosun HS510C and HE510C models
• Mounting: Fits between 510C and QD mount
• Included: Mounting hardware and installation tool
• Weight: Approximately 1.5 ounces

NOTE: Does not perfectly match to 510 FDE red dots sight, please check image posted.