Iain
There is a particular name for the thread form, and it still is availible in larger sizes, that is for pipe of 3inch and above, but no longer availible in the smaller sizes.
Given that your lifter has the suction nipple threaded in the body of the iron casting, I would be tempted to see if it will unscrew, the thread in the body of the casting is likely to be BSP. You can then fit a totally BSP hex nipple and will then be able to buy a BSP tail and nut off the shelf for buttons
http://www.ebay.co.uk/itm/2-BSP-TAIL...item3cc26a125d various sizes availible, I guess 1 1/2 or 1/3/4 would be most appropriate?
Another option if the existing nipple will not unscrew would be to cut off the course thread, open out as much as you dare and internally thread what is left and make buy a male/male nipple to suit, this may restrict the flow a little bit, but I bet you would hardly notice.