Milton 1/4" NPT Mini Filter-Reducer Piggyback Duo S-1142. 1/4" NPT Mini filter-reducer piggyback duo is recommended when space is a problem. Duo offers most of the same features as the full size units. Preassembled with 0-160 PSI gage # 1189. Piggyback mini FR Duo is ideal for use in compact air flow applications. Maximum pressure 150 PSI and Maximum SCFM 21. Preassembled with Milton #1189 gauge.