To impose liability for breach of the implied warranty of merchantability, it is ordinarily necessary to show that there was a defect in the product and that this defect made the product not fit for its normal use and that this caused the plaintiff’s harm. A product may be defective because there is:

• a manufacturing defect,
• a design defect,
• inadequate instruction on how to use the product, or
• inadequate warning against dangers involved in using the product.

If the manufacturer’s blueprint shows that there should be two bolts at a particular place on the property and the factory puts in only one bolt, there is a manufacturing defect. If the two bolts are put in but the product breaks because four bolts are required to provide sufficient strength, there is no manufacturing defect, but there is a design defect. A product that is properly designed and properly manufactured may be dangerous because the user is not given sufficient instructions on how to use the product. Also, a product is defective if there is a danger that is not obvious and there is no warning at all or a warning that does not describe the full danger.