Mark ( bearbrass) and I have been tossing around on whether to retrofit a domed crystal to our red subs. I understand that the #19 will fit ok but there could be a problem fitting a Super Dome #39 that is normally seen on the 1665 SD's. There is also a difference between NOS domes and the new replacement Domes fitted by Rolex. The older models had a very high dome without the vertical sides as seen on the replacement versions. After a LOT of research it seems that the NOS domes can be brittle after all these years and will develop hairline cracks at the base due to the pressure applied by the retaining ring. Not good if you want to wear your watch everyday in all conditions. I guess this is the reason why Rolex fit new replacement crystals at every service for the vintage plexiglass models. Another problem retrofitting a 39 to a 1680 Sub is that the crystal can be very tight to put on due to the retaining ring being slightly out of shape. There is very little room for error and they are not easily fitted. All NOS plexiglass crystals come in the wax paper envelopes to my knowledge and fetch a far higher price than the replacement domes. The replacement crystals are found in the plastic packets. After some thought, I will not be fitting a dome to the red sub if it increases the possibility of moisture entering the watch. Here is a great article posted by Arthur aka AAKVIPER over at VRF. I have been receiving emails from forum members regarding my opinion on the waterproof or water-resistant status of dome crystals in general. Just for general info I will post my findings on the forum. What I discovered, will not probably agree with many forums members. Rolex domed crystals ages from 30 to 60 years old that are attached to any Rolex watch, should not be treated as being waterproof or water resistant! These crystals are purely an aesthetic attachment to any vintage watch and will not prevent humility, perspiration(arm sweat)from entering a watch case via the crystal retaining ring and case lip area. Being a watchmaker I had and still have a few super domed in NOS packages in my parts collection. I have done some extensive water pressure tests over the years on many different age and timeline domed crystals from existing on a watch, to NOS parts from the 1960's and 1970'S still in factory packages. Every domed crystal has failed a proper water pressure test in my shop over the years. I was very intrigued as to why this was occurring. I found that the weak link was the hairline cracks that occur at the base of the crystal because, of the tremendous force of the crystal retaining ring to the case crystal lip. This sandwiched domed crystal base after many years of pressure just gives out to fatigue and time. The result is component failure by these hairline cracks which eventually let in humidity and perspiration which at first cannot be seen by the human eye. Movement and dials are compromised by this seepage. That is why some dials become brown in color and oxidized movement coated parts come about. The NOS domed crystals being over 30 years old also develop these hairline cracks. The bezel press can be a cruel mistress to an aged crystal. The stress of the crystal retaining dye from the bezel press pinches the crystal and causes very tiny hairline cracks which spread over time. About eight years ago I wanted the domed look on an early gloss gilt SWISS four line 5512 as most collectors now try to emulate. So with the intention to really wear the watch in the rain and on a hot summer day. I broke down and used a brand new NOS in package super domed crystal. I removed the 1530 caliber out of the 5512 case, then administered the water pressure test on the case to only 100 feet with this never on a watch super dome crystal. It passed with flying colors. I was very pleased and I felt that the dial and caliber were safe from the outside elements. Then a year later I was walking with the same 5512 in the rain having fun in Manhattan. I took a glance at the dial for the correct time, and noticed the domed crystal had some mist on the top of the inside crystal area. I was bamboozled to say the lest. I was sure that some twin lock crown and tube gasket failure had occurred. The next day I removed the 1530 movement from the 5512, and tested the complete case sans caliber. To my surprise bubbles were streaming from many areas where the domed crystal and crystal retaining ring. The crystal was compromised by the spreading cracks which were visible when I took the retaining ring off, and inspected it with a loupe. Of course I asked a few seasoned watchmakers as why this was occurring to brand new domed crystals? They basically responded that age weakens the crystal and they become somewhat brittle. That is why Rolex service always recommends a new crystal with a service to back up the waterproof claim. The bottom line is, any domed crystal in my opinion must be treated as not being a waterproof component. As for me all my vintage watches which I wear in the real world have new crystals. I gave up the vintage look for most of my watches, in order to protect the dial and movement. Domed crystals are an outstanding touch to any vintage watch, and make the watch historically correct. But like with any old part, it should not be expected to perform like a new component. Arthur Here's a few pics of various domes on a 1680 Submariner - borrowed from VRF.