M4 Mag Tube ID

[kmc0929]

Trying to ID the tube that came on my gun, looks parkerized - and right near where the threads meet the receiver it says US. The previous owner says he got it from SWFA? The follow is red. Any clue what parts these are? Is the follower factory or US?

[needncash]

Post pictures to help identify the parts in question. The OE follower is black & red and Brownells sells a red anodized aluminum follower.