Don't sweat this either...
The center hole is threaded and is used to install the harmonic balancer. NEVER use a hammer.
Always take care to protect the crank threads.
Also be aware that there are several styles of harmonic balancers and the bolts can be a different length. Make sure your bolt is long enough. I know a guy who had a truck balancer held on with an auto balancer bolt that only grabbed with one thread and it pulled out. Eventually he dumped the balancer and chewed up the end of the crank and made a mess out of the lower front area of his truck. Don't be afraid, just be sure......
Some instructions are here:

http://www.powerdyne.com/manuals/K10415.PDF

Hope it helps,
Jeff

Originally posted by oldways
i am also confused about another aspect the lower pully mounts onto the harmonic balancer and that mounts onto the crank on my engine it looks like there is a bolt missing right there in the centre. the shop i got this from says no!! man i looked in there and there is thread and all please help....