Part of Mickey's attempts to fix the Border House's plumbing, the clamp is secured around a leaky pipe on the pressurized machinery outside the front door. To remove it, April needs to complete the puzzle to de-pressurize the system (only mildly less annoying than the steam puzzle in Syberia 2).
Later, the clamp is a key component in April's subterranean fishing trip. Along with some unexpected accessories. (The Rubber ducky puzzle is reviled by some players as the most illogical puzzle in The Longest Journey.)
Obtained from the pipework outside the Border House.