Do I need clamps for this hose, and what size?

You'll need hose clamps at both ends—one for the 3-inch side and one for the 4-inch side. Clamps are not included, so grab stainless steel units sized to match your barbed fittings or ports.

Can this hose handle boost and coolant both, or should I pick one?

Silicone handles both coolant and turbo boost without issue. Use it wherever you need that diameter step-down—intercooler piping, radiator hoses, intake manifold runners, all fair game.

What's the difference between this 3-ply and cheaper 1-ply silicone hoses?

Three plies mean more burst resistance and better shape retention under pressure and heat cycling. You're not buying a generic tube here—the reinforcement is real, and it shows in longevity.