That would be a huge help, thank you IamOiman!

Why? Do you think Roberta Bosco doesn't know what shes talking about?

??

It's because he is the easiest to reach for me. Roberta will respond by email but sometimes it takes a few days. From how I interpret this thread Jonathan would like to acquire one of their springs if possible. After correcting my intitial statement that Bosco uses standard springs with your insight, it would not hurt to ask them or the suppliers for one of their specific springs like you mentioned John

Someone posted awhile back that they tried to order a spring or 4 seal piston (I forget which) directly from the factory & they wouldn't take the order as they didn't own a Bosco. It's unlikely any U.S. distributor would stock a spring but they might order it although the cost with shipping might be high for what you might gain. Roberta calls it a 9 bar spring but it peaks right around 8 bar. How different is that from the single spring in a Pro 800 or Londinium??

I have a pressure gauge on my grouphead and the highest I've been able to hit is 7 bar. If there's a single spring out there that's able to hit 9 bar then I'd buy it, hence the reason why I asked.

What did it hit with the smaller spring installed? The Pro 800 uses a dual spring set up doesn't it? I've measured a peak of 8 bar with my Sorrento single spring. I don't believe any of the springs in the current crop of spring levers will hit 9 bar with one spring. Why would you want it to go that high?

Roberta told me that the total contribution of the inner spring in their dual spring set up is small as they don't like high pressure extractions so even their dual spring configuration is different from other manufacturers. If you want more then 8 bar perhaps you should try to buy both springs.

When I bought the group head with pressure gauge I had it configured with one spring only, for me to measure it with 2 springs I'd have to take my old group head apart, which I might do just to get an idea, but from what I remember reading people were getting 10-11 with both springs installed.
As far as why I want 9 bars... because I'd like to experiment, that's all.

Is the pressure gauge on your 800 the naked one?

Yep, that's the one.