A heavy duty shock is now standard for user weights greater than 220 lb on the M3 Corpus. Factory default shock settings on the M3 Corpus shock are as follows: less than 220 lb = A [STANDARD], 220 – 265 lb = B [HD], greater than 265 lb = C [HD]. The M5 Corpus utilizes one shock for all user weight ranges with the same settings as used on the M3. For vent tray applications, the HD shock is required on the M3 Corpus. A “C” shock setting should always be used when a ventilator tray is installed.