The following are specifications of the mounting screws for the bottom panel of the HPD-15. These would be used for mounting the HPD-15 to the PDS-10 stand.
10/32
No longer than 1-1/2"
Caution: Using the wrong size screw can damage the HPD-15. It is strongly recommended to order these screws directly from Roland's parts department if you're unable to obtain them locally.
The parts department can be reached M-F 8:00-4:00pm Pacific time at 323-890-3771.
Request part number 17041819.