Here are two types of locking differentials side by side. On the left is a forged aftermarket unit, a thicker, more durable piece with a sprag-style clutch that hooks up when we get the power on. On the right is a stock four-pinion clutch pack unit as found in Limited-Slip and Traction-Lok differentials. The factory Traction-Lok unit can take up to 350-400 horsepower. If you need a good life insurance policy, opt for the aftermarket unit. Street drivers should not be fitted with a Detroit Locker (not shown here), which is horribly noisy in turns. Detroit Lockers are ideal for race cars, but not street cars.