I think you may mean a knife with a blood groove, as I am not familiar with anything called a blood gage knife. A blood groove is the colloquial name for the hollowed out strip on some knives. You can see it on the KA-BAR USMC fighting knife, for instance. The proper term for that strip is a fuller. Some people call it a blood groove because they think it is to help drain blood away from the tip of the knife when it is used in combat. Really, a fuller just takes some weight away from a heavy knife without reducing the strength of the blade.
20 gauge is larger
The difference between screw gauge and spherometer is that spherometer can measure the dimensions of spherical surfaces but screw gauge cannot
The size of the bore.
A pressure gauge indicates actual pressure and a differential pressure gauge indicates the difference in pressure.
Size of the bore.
16 gauge is thicker than 18 gauge.
12 has a bigger bore.
Size of the bore. 12 gauge is bigger.
Size of bore, size of ammuntion
A pressure gauge measures blow, a vacuum gauges measures suck
They are different sizes.
26 gauge is your common metal mailbox 26 gauge is comparable to the skin on an elevator door.