While giving discourse to Arjuna, Sri Krishna says that he was VAJRA among weapons.
आयुधानामहं वज्रं धेनूनामस्मि कामधुक्।
प्रजनश्चास्मि कन्दर्पः सर्पाणामस्मि वासुकिः।।10.28।।
Of the weapons,I am the Vajra [of Indra]; of the cows, I am the Wish-fullfilling Cow [of the heaven]; of the progenitors, I am Kandarpa (the god-of-love); of the serpents, I am Vasuki.
In the Chapter 10 of Srimad Bhagavad Gita, Sri Krishna compares himself to greatest among various living/non-living beings, viz., among Adityas - vishnu;; among birds - Garuda, etc.
Now the question is - why did he not mention about Sudarsana Chakra, the weapon of Vishnu (or) Trishula of Shiva, which are considered to be SUPREME, but mentioned about VAJRA, the weapon of Indra?