This post links to RAnn's Sunday Snippets.
like that but closer
Let's talk about cars. More specifically, their engines. Even more specifically, their connecting rods. The connecting rods transfer the up-and-down energy of the pistons into rotating energy at the crankshaft, which then makes the wheels turn and all that (like so). Of course the rods are under terrific stress, and if one fails it usually ruins the engine.
Until recently, a typical connecting rod was made of four pieces seen at the lower left, with the pins resisting the side-to-side stress between the rod and cap. Nowadays, many connecting rods are made per the example at lower right: each one is forged as a single piece. Then the cap is carefully cracked off, and reattached around the crankshaft for a virtually perfect fit without needing any pins. The cracked cap and the rod it is taken from are so uniquely mated that no other cap will fit that rod; and when put together, the crack is practically invisible.
Which reminds me of this: "It is not good that the man should be alone; I will make him a helper fit for him." So the LORD God caused a deep sleep to fall upon the man, and while he slept took one of his ribs and closed up its place with flesh; 22 and the rib which the LORD God had taken from the man he made into a woman and brought her to the man. 23 Then the man said, "This at last is bone of my bones and flesh of my flesh; she shall be called Woman, because she was taken out of Man." 24 Therefore a man leaves his father and his mother and cleaves to his wife, and they become one flesh."