Documents required for My parents to attend my grad walk

Hello, can anyone help me

Iam currently on F1-opt applying h1, i have grad walk in may and would like to invite my parents for grad walk!! what are the documents checklist for my parentsfor visa interview. iam not sponsoring them.i sent grad walk invitation letters. please let me know what documents are required from me to them and what they must have.

thanks in advance

please do reply !!!