What You'll Get
Choose from Three Options
- $29 for one roadside-service trip ($60 value)
- $55 for two roadside-service trips ($120 value)
- $85 for three roadside-service trips ($180 value)
- Choose one of the following for each trip: lockout, fuel delivery, tire change, or battery jump.
Pin-and-Tumbler Locks: Lining Up for Entry
The seemingly random ridges on your keys are actually a code that tells a lock how to open. Read on to learn more about how a common type of lock lets you in—and keeps burglars out.
Since its invention in the 19th century, the average pin-and-tumbler door lock has remained remarkably trustworthy: put the right key in and the lock grants you entry. Put the wrong key in and no dice—like clockwork, every time. The lock works through a feat of simple mechanical engineering. Inside the lock is a cylinder that rotates to move the deadbolt in and out. The purpose of a lock is to keep that cylinder from turning when it isn’t supposed to—an obstacle it achieves via five or six spring-loaded pins that block the cylinder’s rotation. At rest, with no key in the lock, the pins cascade into the keyhole at varying lengths. The length of these pins correspond precisely to a key’s serrated ridges, which, when inserted into the keyhole, align the pins so that they form a single, seamless gap known as the shear line. Only then will the cylinder be able to rotate and disengage the lock. With the wrong key, the pin heights won’t align correctly, preventing the cylinder from turning and keeping intruders from watching your parents’ cable while they’re out of town.
Of course, the pin-and-tumbler mechanism is just one of many varieties of locks, and in fact its design wasn’t even particularly groundbreaking. The inventor, Linus Yale, drew inspiration from a large wooden version used in ancient Egypt some 4,000 years prior.
The Fine Print
Promotional value expires 180 days after purchase. Amount paid never expires. May be repurchased every 30 days. Valid only within 13 miles of zip code 28217. Appointment required, same day appointments accepted. Limit 1 per person, may buy 1 additional as gift. Valid only for option purchased. All goods or services must be used by the same person. Call to schedule assistance. Offer is not valid for towing. Offer is not valid for commercial vehicles. Merchant is solely responsible to purchasers for the care and quality of the advertised goods and services.