Collet identification and availability.(Long Shot) Myford own?

[WorkshopChris]

This is a long shot but does anyone recognize this collet its from a early Myford cylindrical grinder and is fitted to the workhead.
If anyone recognises it i can get some accurate dimensions,it is threaded internally.

The machine dates form 1959.
4c collets were fitted to the newer machines, i have been looking for a while without much luck.
I have just come across the original documents with a delivery date of 12 Nov 59.
I am wondering if i could modify a ER20 collet holder to somehow fit or hold in the existing 1/2" collet to give me the ability to hold small metric parts.

 

[optima21]

not sure about the collets you have but you should be able to modify a ER20 collet chuck to fit. I'd start off with a 2MT one as there is enough metal to turn them down to 1/2" and the bore on mine is 8mm so that would leave just over 2mm wall thickness. you can get ER20 collet holders with 5mm bores for mounting on motor shafts, but they may be too short to be useful for your purposes. you can also get straight shank collet holders but the bores will be too big to leave any metal to to in the collet holder you have. with the ER20 collet holders you can grip upto 13mm diameter.

just thinking about it, if you have a bit of spare time, making a collet holder is a nice little project, I've made an er20 collet holder in the same way as Doubleboost has in this video.