Omnitech 16878-US what is the end size for external GPS antenna?

Hi
I was not sure where to post this. I have Omnitech 16878-US with Windows CE 5. I see there is an external antenna jack in the back. I would like to try it out.
Any idea what size / type it is?

Thanks

Did you try using a Google search?

Yes I did
Looks like

Anyone know what type of end is needed for this size?

Thanks