Slant Six and three on a tree.... oil and water; optional 
(a detuned performance motor )
The difference may be in the hardness though they should be kinda close, how it's done can differ.
The black ones may be harder but usually more brittle. I find they don't like being stressed open too far and may snap randomly over time if stretcched and held.
You might test one by twisting it up with pliars. If it twists, it won't likely break out of the blue (usually the bright/silver ones are softer)
Grinding on the E-clip bump stops tweaking, & thrust surface runout that occurs when they are stretched open; it increases the Es inner diameter so it can flatten at or near 100%.
