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I am making a PCB with Eagle and I need to place some leds SMD size 1206. Looking components, I see two different types of LEDs in this size: SML and SMT. Eagle components are LEDSML1206 and LEDSMT1206. Could anyone tell me the difference between them exactly?
Also happens something similar with resistors. In this case are R-EU_R1206 and R-EU_M1206.
Don't waste time on the libraries that come with Eagle. They were created by various different people, don't follow any coherent conventions, and won't likely work with your conventions for BOM information, generating the assembly drawing, parts locator, in-house part numbers, etc.
When in doubt, go make your own library part. It's a useful skill on its own, and once you've learned it, it's quite easy to do.
By the way, unless these are power LEDs, you're probably better off using 0603 types. Those tend to be cheaper and more available than 1206.
SML appears to be a Lumex specific acronym or part number. I wouldn't put much faith in the library parts you've found.
Instead, read the data sheet for the PCB layout and compare it to the pad layout of the various parts that should fit in the library, or create your own.
Chances are good that you could choose either and it will work in most processes, but a lot of hobbyists create pad layouts that are not optimal for all processes, and some even make bad layouts on purpose to support a specific process - for instance some will create huge pads that are easier to solder by hand because the part doesn't cover more than 10% of the pad, so there's room for the soldering iron tip. Unfortunately those pads can rob the joint of solder under many production processes, and people going from prototype to production find significant issues in process or reliability.
If this is a one-off project, you can probably use either pad, or even a generic 1206 pad, but the best practice is to read the data sheet and compare or make your own part.
It's fairly simple and easy in Eagle, so much so that making your own might be easier and faster than comparing the existing ones to the data sheet.
