For vintage car enthusiasts and collectors, this is a rare find - a brand new, in-box Defiance No. SD 16 spark plug. Made in the United States, this box of. 10mm spark plugs is a perfect addition to any vintage spark plug collection. The spark plug is designed to fit a variety of antique cars and is a great display item for car enthusiasts. This particular spark plug is part of the Defiance No. SD 16 Cold series and would make a great addition to any automobile memorabilia collection.