The .frig or Fox Rig format is believed to be used to set up IK groups for .fmdl files.

Header

• 0x0 - 0x3 (uint32): Signature.

• 0x4 - 0x7 (uint32): Header length.

• 0x8 - 0xB (uint32): Unknown.

• 0xC - 0xF (uint32): Num Entries?
• 0x10 - 0x13 (uint32): Unknown.
• 0x14 - 0x17 (uint32): File length.
• 0x18 - 0x1B (uint32): Offset for bone hash section.
• 0x1C - 0x1F (uint32): Offset for unknown section.

Unknown Section Info

• 0x0 - 0x3 (uint32): Unknown.
• 0x4 - 0x7 (uint32): Num entries.
• 0x8 - (0x8 + 0x4 * num entries - 1) (uint32[]): Entry offsets.

Unknown Section Data

• 0x0 - 0x3 (uint32): Unknown
• 0x4 - 0x11 (string): Name.
• 0x12 - 0x57 (binary32[]): Unknown.

Bone Hash Section Info

• 0x0 - 0x3 (uint32): Num entries.

Bone Hash Section Data

• 0x0 - 0x3 (uint32): Unknown.
• 0x4 - 0x7 (uint32): Truncated bone hash.