The Ashoka Chakra is a depiction of the Dharmachakra represented with 24 spokes. Ashoka Chakra is also present in the centre of Indian National Flag where it has replaced the Charkha(the spinning wheel) of the pre-independence version of the Indian Flag.
Reason for 24 spokes on the Chakra:
According to Hindu religion, Puranas mentioned that only 24 Rishis wielded the whole power of the Gayatri Mantra. These 24 rishi in Himalayas are represented through the 24 letters of Gayatri Mantra. The all the 24 spokes of Dharmachakra are representation of all these 24 rishi of Himalayas in which Vishvamitra is first and Yajnavalkya is last who governs the religion (Dharma).
Ashok Chakra is symbol of Dharmachakra and also known as Samay Chakra in which all the 24 spokes represented 24 hours of the day and symbol of the movement of the time.