Outside diameter for thread size M12 x 1.75 is 16mm x 2 mm wall thickness Outside diameter for thread size M16 x 2 is 20 mm x 2.5 mm wall thickness. Extension Tubes. These extension tubes are ideal for extending the length of a variety of float switches. Ideal for use with the plastic type float switches. Extends the Reach of Various Float Switches Gaskets Made of Nitrile Polypropylene Extensions with M12 or M16 Thread