This stanchion has the newer style "high/low" stanchion base. Other high/low base stanchions use a 1/2" through bolt which mounts on top of the toerail. This stanchion substitutes a tube with a male thread for the through bolt. The vent hose clamps onto the tube, a nut threads on to secure the stanchion to the toerail. Two additional bolts mount through the deck. A hole through the side of the stanchion vents the tank.
This example is from Catalina 30s starting with hull #4726. Other recent Catalinas like the Catalina 270, later Catalina 28s, the Catalina 310 and the Catalina 320 use the same stanchions.
• Top of toerail to top of stanchion: 23-1/2"
• Top of toerail to center of top lifeline: 23"
• High/low offset from deck to top of toerail: 1"
• Tubing diameter: 1"
• Main fastener stud diameter: 1/2"-13
• Main fastener stud length: 2-7/8"
• Inboard support fastener diameter: 1/4"
• Inboard fastener hole horizontal offset from main stud: 2-1/4" center to center
• Center to center between deck fasteners: 2-1/8"