These are US Battle Dress Uniform (BDU) trouser blousers, better known to British troops as 'Twists'.

Despite being prominently marked 'Made in China' on the packaging, these were bought, by me, from a US PX uniform shop in the USA - and it does not get much more authentic than that! 

The packs each contain 2 elasticated twists with hooks at each end. They are designed to go around the top of the combat boot so that the bottom of the combat trouser legs can be tucked up into them (see photos) to give the familiar neat look to the uniform, retain body heat and keep debris and assorted creepy crawlies from running up your leg.

These are also used by British troops, although never issued, these are usually for sale in PRI shops and have been in general use since at least the mid 1970's.

New and unissued condition. Unit of sale 1 pair (2 'twists').

Stock No; Uniforms 2