Wolverine MTW M4 Receiver Tensioning Screw

Upper and lower receivers are made to tolerances that have to allow assembly, which means there is nearly always a little play left over. A tensioning screw closes that gap by pushing the two halves apart from the inside until the fit is snug.

It matters more on an HPA build than people expect. A receiver that moves under recoil also moves the hop unit and the feed path relative to each other, and the result reads on target as inconsistency rather than as a loose gun.

These are also the first thing to go missing. The screw is small, it lives somewhere you only visit during a strip, and a replacement costs less than the postage on it — so it is worth adding to an order rather than ordering on its own.

Specifications

Good to know before you buy

Snug, not tight. The screw is there to take up slack, and winding it hard against the upper puts load into a receiver face that was not designed to carry it.

Check the fit with the engine in. Tensioning an empty lower can feel right and then go slack once everything is torqued up, so set it on the assembled rifle.

Frequently asked questions

What does a tensioning screw actually do?
It pushes the upper and lower apart from inside the receiver so the designed-in clearance is taken up and the two stop knocking against each other.

Will it fix a badly worn receiver?
No. It takes up normal manufacturing clearance. Genuine wear or a damaged pin hole needs the part replaced rather than tensioned.

Does it suit the MTW-9 or the MTW-308?
This is the M4 item. Tell us which rifle you have and we will confirm the right part before you order.

How tight should it be?
Until the play disappears and no further. You are removing a rattle, not clamping the rifle together.