Shiva Dhanush

"Pinaka" is the bow of Lord Shiva, however it is not the same as "shiva dhanush" mentioned in Valmiki Ramayana. Pinaka is the original bow of Shiva used for total destruction or "Pralaya". As per original Valmiki Ramayana, two bows were created by God Devendra of equal capacity which were given to Rudra and Vishnu and requested them to fight with each other to know who is the powerful one. However just before the start of the war an Aakashvani said that the war will lead to total destruction and hence the war was stopped. On hearing Aakashvani, Rudra threw his Dhanush which fell on earth to be later known as "Shiva dhanush". It was later found by King Devaraatha, the ancestor of King Janaka. It is mentioned in the Hindu epic Ramayana, when its hero Rama (another avatar of Vishnu) breaks it to win Janaka's daughter as his wife.

Vishwakarma crafted two divine bows. He gave Sharanga to Lord Vishnu and Pinaka to Lord Shiva . King Janaka of Mithila had a daughter named Sita. In earlier part of her life, Sita while playing with her sisters had unknowingly lifted the table over which the bow had been placed; which was something no one in the kingdom could do. This incident was however observed by Janaka and he decided to make this incident as the backdrop for swayamvara.

Later, Janaka had announced that whosoever wanted to marry Sita had to lift the divine bow and string it. The bow was broken by Ayodhya's prince Rama when he attempted to string the bow, during the swayamvara of Sita, thereby winning the princess's hand in marriage. After the marriage when his father Dasharatha was returning to Ayodhya with Rama, Parashurama obstructed their path and challenged Rama for breaking his guru Shiva's bow. Rama extolled the sage. After that Dasharatha prayed to the sage to forgive him but Parashurama remained enraged and brought out Vishnu's bow. He then asked Rama to string the bow and fight a duel with him. Rama snatches the bow of Vishnu, strings it, places an arrow and points it straight at the challenger's heart. Rama then asks Parashurama what he will give as a target to the arrow. At this point, Parashurama feels himself devoid of his mystical energy. He realizes that Rama is the avatar of Vishnu, his successor and his superior. He accepts Rama's superiority.

...
Wikipedia