ATA, Comp M5 (Adjustable Turret cap, Aimpoint Comp M5)  is a simple and robust solution.  ATA, Comp M5 gives the user the ability to make adjustments to either the windage or elevation without removing the caps. 

ATA, Comp M5consists of a pair of 17-4 SS billet machined cap with internal O ring, and a 17-4 SS rotating disc with an externally accessible top slot.  The disc has two dots/protrusions that mate perfectly with the two indentations of the adjustment dial on the sight.  To make adjustments to either the windage or elevation, the user uses the rim of a cartridge (.223, .308, .45 ACP, and 9mm were tested) or a coin to rotate the externally accessible disc of the ATA, Comp M5. 

ATA, Comp M5 caps are serrated to assist in its installation.  There are 12 serrations total, matching the tick marks on the inside of the factory T1 cap.

The internal O ring prevents undue moisture from entering the ATA, Comp M5. In water immersion testing, ATA, Comp M5's ability to keep out water is on par with the single piece factory cap, to the depth of 77ft.  To wit, T1 and T2 windage and elevation adjustments are water resistant even without the caps, they can't be taken to Aimpoint specified depths without the caps on, Aimpoint only warranties the sights to the advertised depths with the caps installed.  When installing the ATA, Comp M5, please do not remove the O rings already present on the sight.

ATA, Comp M5 is billet machined in 17-4 stainless steel, and QPQ treated.  ATA, Comp M5 is shipped partially assembled (O ring is installed inside the cap, the disc is not installed inside the cap).  It is far faster and easier to install the ATA, Comp M5 on the sight with the cap and disc separated (instructions are provided on the back of the card).

In place of the factory marking UP/R with a counter clockwise arrow, ATA, Comp M5's discs have the counter clockwise arrow, but individual caps for UP and R.  As much as it may seem common sense that the elevation adjustment is always on top, and the windage adjustment is always on the side, the marking UP/R can be confusing to new shooters.  At the risk of being redundant, the ATA, Comp M5's disc with the UP engraving is installed on top (for elevation), the disc with R engraving is installed on the right side (for windage).