Thanks for reply. I am familiar with rigid tapping. - However I am really enthusiastic to try this head out. Some details follow :-
The head is an obscure Yamatokoki Manf. Co. unit with the prefix NEWS. It is well engineered and the auto reverse functions more or less perfectly on a pillar drill. - Axial retraction about 20mm. Forward and reverse are geared 1:1. Fitted with a stop rod beside the quill. It resembles a Procunier. Have assumed it is a cone type unit.