I just received, haven't installed an Aqua Step on my 96GTI, it came with 6ea. 1-1/2" stainless self tapping screws, not sure about the diameter but the instructions say to use a 3/16" drill bit and to use a drill stop and drill no deeper hole than the length of the screw. So I am assuming that the hull is 1-1/2" thick where the step mounts. My kit also includes 6 nylon washers that goes between the bracket and the screws. It also includes 2 angles plastic blocks (shims0 to allow for the slant of the hull where the step mounts.
Aqua Step is the OEM manufacturer for SeaDoo.
To confuse you further the instructions also say that your kit could come with "AVK" inserts, mine didn't.
From your Avatar pic. I'm thinking you have about 95's GTS which I think is the same hull as mine, so it should be the same hardware as I received.
AquaStep website is
www.aquaperformance.com Phone no. 951-940-9425.
Here's the instructions:
http://www.aquaperformance.com/apimages/ap_pdfs/apwatercraft_instructions.pdf
Let me know how you come out if you need the instruction sheet let me know. You can get the screws at Lowes but you will need the plastic shims for a good installation. Check and see if it says AquaStep on one of the brackets.
Lou