A handheld power tool having a detachable tool head is disclosed in which, depending on the type of tool head used, selection of reverse movement of the rotary assembly of the power tool can be prevented. Where reverse movement of the tool head is undesirable, such as for a saw blade, the tool head contains a contact plate that slides a plate member to a position to prevent selection of the reverse direction by the user. However, where reverse movement of a tool head is desired, such as for a drill head, the plate member remains in its original position such that forward and reverse directions can be selected by a user.