Omega Speedmaster chronographe vintage cadran noir

I have a question for some of the repair people out there...Are Hamilton Crown Tubes threaded into place, or tension fitted into place. Specifically, I am thinking about a Hamilton Barrel Plain that needs a new crown tube.How do I go about getting a properly fitting crown tube? I will likely order from a parts house, but I wonder how to get the color/shade/patina to match, or simply not worry about it since it will likely be covered by the crown.I knowit's a very specific question, but the folks........

In fact, with eBay, you need more than a "bit".. Shortly after I snagged a Seiko World Time GMT desk clock from the 70s on the bay of badness the seller jovially contacted me to inform me that he'd just nicked the pics from the www for the auction but the clock I would be receiving was "even better" and that I should really look after it as it had belonged to his Grand Dad. Oh boy.. My heart sank and I sat back and waited for inevitable pile of junk to arrive on my doorstep. So as I opened the b........