The Monofilament Wires are weapons used by Walter C. Dornez.
Walter's are ultra-sharp and super-thin, so much so that they can hardly be seen by the naked eye. Even Vampires like Jan Valentine failed to see them, despite his senses being enhanced, until it was too late, allowing Walter to painfully yank the ring off of his lip. They are embedded into his gloves and are what he uses as his primary weapon. According to the Hellsing Official Guidebook, Walter's wires are made of a special steel.
As a human, Walter appeared to draw the wires either from or through the material of the gloves he constantly wore, and the wires appeared to originate from both his fingertips and from the bases of his fingers. As a vampire, he traded in his fingered gloves for a pair of fingerless ones with what appeared to be metal bands encompassing the bases of his fingers. He also had fingerless gloves back in The Dawn. The wires were seen to protrude from these metal bands, but the wires also appeared in many instances to protrude from the skin of Walter's bare fingertips. The only time Walter was ever seen to directly generate the wires, he very clearly pulled a set of them out of several ungloved portions of his hands including the fingertips, and out of both the metal rings around the bases of his fingers and the palms of his hands.
The wires are extremely deadly, able to cut through almost anything from an entire squadron of ghouls, steel, to entire buildings, with ease. They also appear to be blessed, considering their blue-ish glow and ability to kill vampires. They can also form a type of mesh-like shield strong enough to deflect bullets and can be rigged into a corpse -- even Baskerville -- and use the person as a puppet. It is unknown who first manufactured them, but it was likely Hellsing; he has been seen using them when he was a teenager fighting for in Hellsing: The Dawn.