Stripes I & II are the names of Stocking's spiritual katanas. Stocking has the ability to transform her stockings into a pair of katanas, which can be used to battle ghosts. She first referred to them by name in "High School Nudical".
Stripes I & II can be attached at the base of the hilt, to attack in a similar way to how a helicopter's rotors work. Her katanas are able to hurt any spiritual being, such as angels, demons and ghosts.
Like any other sword, Stripes I & II must be sharpened, and if not properly cared for, can break. Stocking is also unable to transform her stockings if they are stretched, as seen in "The Diet Syndrome".
Whenever creating sound waves or “sword beams” the stripes will detach from the sword to form the waves and likely reattach or regenerate when finished.
It's assumed that Stocking can transform her stockings into any other type of swords, but such is yet to be seen.
The mangas may not properly be considered part of the “canon” but there is a manga where Panty and Stocking steal Scanty’s and Kneesocks’ garments (albeit alternate clothing) to form weapons. Panty makes a gun as usual while Stocking creates an axe or scythe-like weapon. So in this depiction her weaponry isn’t limited to just swords but can turn into different sharp weapons.
The english dub doesn't say the weapons name directly.