Newbie UG Polerouter Jet

I recently purchased a Polerouter Jet from ebay and I was hoping you guys could give me some advice. It is missing the inner rehaut/chapter ring. I haven't received the watch yet and I'd like to purchase a chapter ring as soon as possible. It would be greatly appreciated if you could advise me to what size ring it will need. Below I have a link for the watch and also chapter rings for sale. Also, the watch has a 218-9 movement if that helps.

Watch:
http://www.ebay.com.au/itm/60-039-s...OxohjPCSpzN1arvNNRdmw%3D&orig_cvip=true&rt=nc

Chapter rings:
http://www.ebay.com.au/itm/131010769744?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

http://www.ebay.com.au/itm/151310768396?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

Hello,

I have a Polerouter Jet and the case is different from the "classic" Polerouter (date ...).
In the picture below you'll see 4 UG's, the Jet is the third (left from the Monodate).

The case of the Jet is thinner and the lugs are straight.
I saw some with a different case (like yours) on Ebay the past months. I think they are re-case watch.

Maybe someone can clarify the case of the Polerouter Jet, but to be original you may find a NOS case somewhere.
The "Jet" feels lighter on the wrist with this specific case.

For sure you'll need a chapter ring ; )

Edit : Not sure any Jet has a chapter ring.
A picture of the back : Polerouter Jet

Thanks gatorcpa for the info.
what about the case, here is another case design on ebay : 301228710250
but there is no picture of the case back.

And the dial with integrated chapter ring : 181420479619