Quick answer

The RUSAN Modular Adapter MAR securely connects thermal or night vision clip-on devices to your daytime optic. Follow the correct sizing and clamping sequence to maintain repeatable zero and avoid damage.

Why the MAR adapter needs correct sizing

The RUSAN MAR (Modular Adapter Repeatability) uses a clamping mechanism that must match both your clip-on device's objective diameter and your daytime scope's eyepiece. Choosing the wrong diameter can lead to poor alignment, image vignetting, or even physical damage during recoil.

The adapter is available in multiple diameters to fit nearly any combination. Always measure your optic's outer tube diameter at the connection point before ordering, not the lens glass size.

Common mistake: over-tightening the clamp

The MAR clamp is designed for a firm, repeatable grip—not maximum torque. Over-tightening can deform the adapter body or your optic's housing, leading to zero shift or permanent damage. Tighten only until the device is secure and cannot rotate under light hand pressure.

How to mount the RUSAN MAR adapter step by step

  1. 1. Measure and select the correct diameter: Use a caliper to measure the outer diameter of your daytime scope's eyepiece or objective where the adapter will clamp. Match this measurement to the available MAR sizes. Do not guess—a 0.5 mm mismatch can prevent proper clamping. Always measure twice; ordering the wrong size is the most common mistake.
  2. 2. Clean all mating surfaces: Wipe the clamp interior and your optic's surface with a lint-free cloth and isopropyl alcohol. Dirt or oil reduces friction and can cause the adapter to slip under recoil. Even a small oil residue can compromise repeatable zero retention.
  3. 3. Attach the adapter to the clip-on device: Slide the MAR adapter onto the thermal or night vision device's objective housing. Align any index marks if present. Tighten the clamp screws evenly in a cross pattern to avoid tilting the adapter. Uneven tightening can cause the device to sit crooked, shifting your point of aim.
  4. 4. Connect the clip-on to your daytime scope: With the adapter attached to the clip-on, carefully slide the assembly onto your daytime optic's eyepiece. Ensure the clip-on is fully seated and parallel to the scope tube. Tighten the clamp just enough to prevent movement—do not force it. If the fit feels too tight or too loose, re-check your diameter measurement rather than forcing the clamp.
  5. 5. Verify alignment and zero: Look through the daytime scope with the clip-on attached. Confirm the image is centered and free of vignetting. Fire a test shot or use a collimator to check point-of-impact shift. If zero has shifted, re-check the adapter's seating and clamp tension. A correctly mounted MAR adapter should return to zero when removed and reattached—this is the 'repeatability' feature.

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