This pneumatic stop light switch is built for Mack heavy-duty air brake systems. It stays normally open at 0 psig and closes at 5 psig, so the stop lights trigger as soon as air pressure builds in the brake line. Sold individually.Interchanges:1MR3544P225158791Mack 1MR1418RFeaturesPneumatic stop light switchNormally open at 0 psigCloses at 5 psigSold pack of 1 eachTech SpecsPressure: Normally open at 0 psig, closes at 5 psigDimensions (HxWxL): 5 x 1 x 5 in.