Asceticism

Asceticism (Nyas) are of three types - Sthiti (posture) Utpatti (origin) and Laya (fusion).

1. Establishing and chanting the cryptic mantras (alphabets) from the thumb to the little finger is called 'Sthiti nyas'.
2. Establishing and then chanting the cryptic mantras from the right thumb to the left thumb is called "Utpatti nyas'.
3. Establishing and then chanting the cryptic mantras from the left thumb to the right thumb is called 'Laya Nyas'.

'Sthiti' nyas should be practiced by the householders 'Utpatti nyas' should be practiced by the celibates 'Laya nyas' should be practiced by those people who have relinquished the world (Vanprasth).

A widow should practice Sthiti Nyas. An unmarried girl should practice Utapatti Nyas.

http://hinduonline.co/Scriptures/Puranas/ShivaMahaPurana.html