Is it possible to book a visa slot without i20?

Yes you can go ahead and start your ds160 application without having i20 Also you can create your profile on cgifederal for booking the slot

the university details in your visa appointment, without cancelling the appointment, then

can you put a gen 4 ssd in a gen 3 slot You do not need to pay the SEVIS fee to make a visa appointment, but the SEVIS fee must be paid at least three days prior to attending your visa interview at

candy bet slot login You are applying for an initial I-20 The I-20 can be used to apply for an F1 student visa at a US Consulate