Thread forming fittings have special tapered drive threads to reshape the material in an untapped hole to provide a leak proof seal. They are most effectively installed by spinning into the untapped hole, but may be driven straight into the untapped hole. Thread forming fittings can be replaced by any standard threaded fitting or by another thread forming fitting. Alemite® Thread Forming Fitting, Straight, 1/4-28 UNF, 0.97 in Overall Length, 5/16 in Hex