A lockable strap divider comprising a strap receiving portion having side walls and a transverse bar mounted at a central point between the side walls, and a clamping portion pivotally connected to the rear end of the strap receiving portion. There is a clamping device on the two portions for releasably locking the clamping portion over the strap receiving portion. Unlocking the clamping device from the strap receiving portion allows straps threaded through the transverse bar on the strap receiving portion to be adjusted. Locking the clamping portion over the strap receiving portion locks the straps in place. The locking and unlocking of the clamping portion can easily be done while the helmet is still on the wearer's head, so that adjustments can be made without removing the helmet. The adjustments can also usually be done with one hand.