I went to the Schutz valve website and it looks like for the green handle it is a British Standard thread in a S60 x 6 thread.

https://www.schuetz-packaging.net/schuetz-usa/en/spare-parts/discharge-valves/screwable-ball-valve-dn-50-3026204/#?f=%7B%22outletFittingAccessories%22:%7B%22attributes%22:%7B%22type%22:%22dn50%22%7D%7D%7D&t=outletFitting

Johnny was correct, in that it is a buttress fitting:

https://www.globalindustrial.com/p/storage/bins-totes-containers/containers-ibc/s60x6-female-buttress-x-2-male-bsp-pipe-thread-adapter

The size is sure deceiving though! I thought it to be much smaller than that!