astonishingly long time

In many Japanese temples, bamboo nails are used to build cedar and cypress roofs. 

Produced of hard edges of giant trees, they are 3 cm long and 3 mm thick.  Stalks are first heated in large pots so that sap is driven out, which turns the wood very hard and durable.  

In the process, the surface of bamboo also becomes very smooth. That later allows roofers to carry 30-50 nails in their mouths without getting splinters.

A roofer twists individual nail with his tongue, so that the tip points inward and forces it out of his mouth. He then presses on the shingle with his left hand, takes the nail with the thumb and the index finger of his right hand, and pushes it onto a shingle with a small iron plate.

Now he drives the nail in with three or four blows of a hammer. The bamboo nail splays out a little at the head,  thus becoming thicker, which helps to keep the shingles in place.

The bamboo nails last for astonishingly long time. 

(Konchi-in Temple, Kyoto)