From the same as pethen; a stretcher, i.e. A sill -- threshold.
see HEBREW pethen
H4670. miphtan
מִפְתָּן noun [masculine] threshold (compare Late Hebrew מָּתִין cross-beam; ? Arabic carpenter;); — absolute ׳מ 1 Samuel 5:4; Zephaniah 1:9; construct דָּגוֺן מִפְתַּן 1 Samuel 5:5, ׳מ הַבַּיִת Ezekiel 9:3; 10:4, 18; 47:1, ׳מ הַשַּׁצר 46:2.