Glow plug insulators

I have a 24v direct start Model 12 grader with glow plugs.  The outside insulators (Cat calls them Sleeves) are no longer available.Any suggestions about what material to use to make them? 
[attachment=68662]Glow Plug2.jpg[/attachment]

You might be able to adapt a harness assembly from a 3306 engine, 7N9636
https://www.ebay.com/itm/112804213317?epid=26010562851&hash=item1a43a7b245:g:q3QAAOSwM91afI4P

what about engineering nylon you can get it in various round stock sizes. would be hard to make them if you have a lathe or drill press. or use a bit or rubber hose heater or fuel hose would be suitable. or if the attach using a eye tag get the insulator boot off a car with distributor ignition the idea is only to cover them so nothing can accidentally short out.

Hi ? Delta How are you? i had a turner mate of mine make 2 for my old six one was missing one was loose and was burnt pretty bad , i supplied a piece of 7/16 brass hex for the collet and 5/8 for the sleeve couldnt tell the differnce from origanal Lance need four for a factory direct electric start genartor he has I got him to make four for him. the collet is soldered to the wire pushes over the end of the glow plug ,which looks like end of a pencil then the sleeve tightens the collet to end of glow plug he made sleeve and collet if you have lost sleeve it means you dont have the collets either, you put sleeve over the harness wire to each glow plus then solder collet on to wire cant lose the sleeve because collet stops it from falling off wire kel