Wet End, Gecko AquaFlo FMXP2 2.5hp 2"mbt 6.1"dia 56fr

Note: This is a 6.1 wet end. 

56 frame spa wet ends can have one of two designations - 6.1 or 6.3. The difference is the measurement between the top two thru-bolts. 6.1 wet ends measure 4" and 6.3 wet ends measure 4-1/8". See diagram below.