Does not fit my rock river - AIM Sports Inc AR/M4 MLOK Handguard

The hand guard is a good size for small to medium hands - like mine. No directions with unit but I am experienced so not a big problem. However, there is no barrel washer. The thread nut does not mate tight to the receiver unless turned 30 degrees past level. As a result, I cannot complete the installation. I assembled the entire upper - noticed after a bit of handling the hand guard was loose - and had to disassemble the entire upper to see the problem. Until I locate a suitable washer the rifle is dead.