Brake Pump Uprade

Hey guys!

My XS750 gets a makeover and I want to redo the bar controls, brake controls et cetera.
Since I read and heard from a friend that switching the stock brake pump to a 5/8 inch pump will increase the braking power I will try that.
My question is now:
How do I convert the 5/8 inches into MM measurements (the grimeca brake pump I´m looking at is 16MM?is this correct?

Thanks in advance!

I remember 5/8 being 15.8mm, so that should be a 16mm master cylinder

The 5/8" is simply the piston (or bore) diameter so it is a straight imperial to metric conversion. The power delivered by the MC is the ratio of piston area at the MC to the combined piston area at the caliper(s). The larger the ratio, the more mechanical (hydraulic) advantage the MC has over the caliper, so the smaller the piston the greater the ratio and hence more power which means less lever effort. Of course nothing is free, and the trade off is that a smaller piston has to travel farther to move the same volume, so you get an easier to pull brake lever but have to pull it farther. The trade off here is also straight forward - a twice as powerful MC will have a piston with half the cross sectional area and have to move twice as far to move the caliper piston(s) the same distance. To look at it another way, keeping the original MC and adding a second disc and caliper will double the caliper piston area and therefore doubling the ratio. The MC will be twice as powerful, but the lever will have to move twice as far. That is why double discs typically have larger MC bores than single disc systems.