A locking spacer assembly for insertion in a circumferential attachment slot includes a first end piece and a second end piece. The first and second end pieces each comprise an outer surface and an inner surface, the inner surfaces generally facing towards each other when the end pieces are inserted into the attachment slot. An actuator is movable between the inner surfaces and a spacer block is configured to be inserted between the inner surfaces. A fastener is configured to secure the spacer block to the actuator. The actuator is configured to engage the inner surfaces such that the end pieces move toward each other and lock the assembly within the attachment slot.