Air Lift Fittings 21810 Air Lift Company has developed dependable air spring suspension products since our inception in 1949. All our efforts are spent ensuring your safety and comfort by designing, engineering and manufacturing the highest quality suspension products. Air Line Fitting Air Line Fitting; Straight Female; 1/4 in. FNPT x 1/4 in. PTC; DOT; Air Lift Straight Female - 1/4in FNPT X 1/4in PTC