There are several different thread locker materials sold. I use the generic term Loctite, even though Loctite is a brand name. (For years I still called all photocopiers a Xerox machine, regardless of manufacturer.)
The color blue (of the substance, not necessarily the packaging) I think is generic for the variety that you can still unscrew the fastener later. The color does not really matter, but the ability to remove your fastener later is important. I usually refer to it as blue Loctite.
I use it on all rack bolts, all kickstand bolts, and starting last year when I lost a cleat bolt, all shoe cleat bolts too. And of course on my Rohloff hub drain screw after Dave commented that a thread locker also helped avoid dissimilar metal corrosion. It usually already is added to bolts that are threaded into cantilever brake posts, etc., thus I do not bother to add it when it is already there.
But most other bolts, like water bottle cage bolts, seatpost bolts, stem bolts, etc., I use grease instead of a thread locker.
Grease being a lubricant, you do not think of it as something that will keep a bolt from falling out, but it is a viscous fluid, and for that reason it helps reduce loss of bolts and nuts from vibration.
If you use a torque wrench, using different materials on a clean fastener will change the torque necessary to install it, but since I almost never use a torque wrench, that does not matter to me so I have no advice on that topic.
The number 511, I suspect that number is specific to the packaging for a specific country. When Thorn has suggested a specific number, several years ago I tried to find it for sale in USA and it was unavailable but other varieties of Loctite were readily available.
