If it's equivelant to ford pump tool Tool T75L-9480-A , it is for tensioning the belt on the thermactor air pump (the tool moves the pump housing). It is listed for mid 90's Sho engines (eg ford Taurus) , it could very well be an older design than that tho, I don't think ford has changed the air pump design in years.....
NB: The air pump blows extra air into the catalytic convertor to make it finish burning off CO etc.