The APAMPS17MM adapter converts your 17mm mount into a 4-Hole AMPS drill-base mount (mounts, holders, and devices sold separately).  The base measures approximately 2.25 x 1.75 inches.

Simply unscrew the tightening ring to remove the mount’s existing head, then insert the adapter and re-tighten the ring. 

Use the APAMPS17MM adapter with any Arkon mounts utilizing the 17mm ball pattern. Mount devices having a 4-Hole AMPS pattern, including vehicle-specific mounts (VSMs), cameras, GPS devices, audio/video receivers, or satellite radios including Sirius S50, Sirius XM Onyx Plus, XM Onyx EZ, Sirius XM Lynx, Stratus 7, Dock & Play, and Sirius Dock & Play (sold separately).