This is an upset toggle...
http://s7d5.scene7.com/is/image/Fish...id=140&hei=140
'Usually' a toggle is fitted to the tang via the 'open' part of the toggle. With an upset toggle the tang fits through the slot end [and the stay into the open end]. Useful if the tang is quite short.
As for the measurement,stay measurement is usually from chainplate pin center to tang pin center or stay bearing points whichever is stipulated.
Cheers
