The scroll chuck in the photo does not have an insert, it screws straight onto the nose of the lathe. From memory again they were supplied in 30 x 3.8 and 1" x 10tpi, which was the Teknatool standard thread.
Jim
Printable View
That was the first chuck that Teknatool produced. It was designed by a kiwi, ( I forget his name) for turning green tinber. THe timber was turned and let dry when it would assume an irregular shape. The four jaws had two gripping points and worked in compression mode or expansion mode. The "floating" jaws compensated for the irregular shape after drying. The jaws were also bronze to prevent staining on wet timber. It was fitted with an insert that, when screwed in tighter, would force the jaws into expansion mode. This insert when backed off allowed a chromed threaded ring on the front, to be tightened onto the dovetail on the jaws for compression mode. THe chuck held the job very firmly, but needed two pairs of hands to adjust. THe chuck was also supplied with two double ended "C" spanners. It was a good chuck, but a but complicated to use.
Jim