Tubular pin tumbler lock - Design. 1  The design of a tubular lock is similar to the pin tumbler lock, in that there are several stacks of pins. The key is a cylinder shape with notches cut around the outer or (rarely) inner edge. Each of these notches depresses a single pin inside the lock to a specific height allowing the lock cylinder to turn freely.
With more than 31,000 retail locations and the most frequently visited website in the federal government, usps.com, the Postal Service has annual revenue of more than $65 billion and delivers nearly 40 percent of the world's mail.
In order to qualify as a postcard and get the lower rate, however, it must be within certain size limits and of a specific shape. In the US, first class postage for a postcard is about 40% less than first class postage for a letter. Postcards for personal use are typically sent using this standard first class postcard rate.