Internal Wrenching Nuts, also known as an Allenuts or Allen Socket Nuts, are cylindrical nuts that are internally threaded on one end and have an Allen socket on the other end. The outside of the nut is smooth or may have knurling on it. Internal wrenching nuts are used where hex or square nuts won't fit.
Allen Nuts Diameters
Allen Nuts are available on the FCH Network with Imperial/US diameters that range from #1 to 1 and with Metric diameters that range from M5 to 1. The length of Allen Nuts is usually measured from the point to the underside of the head.