A system, comprising: a contact device comprising: a first end configured to couple to a bolt; a second end opposite the first end; and a conductive region between a first insulated region and a second insulated region; and a unit for verifying an amount of thread protrusion of the bolt, the unit comprising a plurality of electrical brushes (175, 180), each of the plurality of electrical brushes (175, 180) arranged to sequentially contact the contact device as the second end of the contact device moves through the unit, wherein the plurality of electrical brushes comprises: a power supply brush configured to apply an electrical current or voltage to the conductive region of the contact device; a first electrical brush configured to generate a first indication of the amount of thread protrusion of the bolt when the second end of the contact device has moved at least a first distance through the unit; a second electrical brush configured to generate a second indication of the amount of thread protrusion of the bolt when the second end of the contact device has moved at least a second distance through the unit; and a third electrical brush configured to generate a third indication of the amount of thread protrusion of the bolt when the second end of the contact device has moved at least a third distance through the unit. a first end configured to couple to a bolt; a second end opposite the first end; and a conductive region between a first insulated region and a second insulated region; and a unit for verifying an amount of thread protrusion of the bolt, the unit comprising a plurality of electrical brushes (175, 180), each of the plurality of electrical brushes (175, 180) arranged to sequentially contact the contact device as the second end of the contact device moves through the unit, wherein the plurality of electrical brushes comprises: a power supply brush configured to apply an electrical current or voltage to the conductive region of the contact device; a first electrical brush configured to generate a first indication of the amount of thread protrusion of the bolt when the second end of the contact device has moved at least a first distance through the unit; a second electrical brush configured to generate a second indication of the amount of thread protrusion of the bolt when the second end of the contact device has moved at least a second distance through the unit; and a third electrical brush configured to generate a third indication of the amount of thread protrusion of the bolt when the second end of the contact device has moved at least a third distance through the unit. a power supply brush configured to apply an electrical current or voltage to the conductive region of the contact device; a first electrical brush configured to generate a first indication of the amount of thread protrusion of the bolt when the second end of the contact device has moved at least a first distance through the unit; a second electrical brush configured to generate a second indication of the amount of thread protrusion of the bolt when the second end of the contact device has moved at least a second distance through the unit; and a third electrical brush configured to generate a third indication of the amount of thread protrusion of the bolt when the second end of the contact device has moved at least a third distance through the unit.