Hercules Prime

A booster with a positional harness made by Thomashilfen, a company with U.S headquarters in Seattle, WA.


This booster seat features a positional harness (non-load-bearing), a very high upper weight limit, compact folding for transfer and storage, and a swivel base for ease of loading/unloading with a lock-out function and up to 10° tilt option.  The booster MUST be used with a vehicle lap-shoulder belt.  The backrest angle adjusts to match the vehicle seatback and can be lengthened as the occupant grows.  The swivel base can be tilted up to 10 degrees; must specify left- or right-ward turning when ordering.  Several accessory guides, positioners, and a stabilizing foot are available to customize fit and function.
Hercules Prime.

Last updated on February 1, 2024.

Child Requirements

  Pounds Kilograms Inches Centimeters Age (years)
Minimum 40 18.1 51.1 129.8 n/a
Maximum 176.4 80 70.9 180.1 n/a

Measurements and Characteristics

Car Seat Mass (Weight)

29.5 lbs / 13.4 kg

Vehicle Fit Characteristics

  Outside height: 34.6 in./88 cm
  Widest outside width: 20.5 in./52 cm
  Vehicle requirements:
  • For comfort, a distance of about 43.3 in/110 cm from the vehicle seat cushion to the roof of the vehicle is recommended for taller occupants. At minimum, there MUST be at least 2 inches/5 cm from the child’s head to the roof of the vehicle. 
  • For stabilization, one of these Thomashilfen accessories must be used:  lower anchors connection (which attaches to vehicle LA bars; required if LAs available) or stabilizing bow (which must fit into the bight when LAs not available).  Depending on best fit to vehicle, stabilizing bow may be installed with the bend either up or down.
  • Requires a level seat cushion that properly supports the bottom of the booster or else the use of Thomashilfen’s accessory “leveling and protection cushion” (Part 513) is recommended (sold separately).

Child Fit Characteristics

  Narrowest torso area: Customizable using shoulder, body or trunk guides
  Narrowest seat cushion width: 15.7 in./40 cm
  Seat cushion depth: 15.7 in./ 40 cm to 18.1 in. / 46 cm
  Seat cushion depth extender options: No

Harness Fit Characteristics

  Harness Type: Five-point  (for positioning only)
  Number of harness height positions: One, but harness height adjusts with backrest, up to 5.1in/13 cm.
  CR bight to lowest shoulder height position: 16.5 in./42 cm
  CR bight to highest shoulder height position: 25.2 in./64 cm
  Crotch strap present: Yes
  Crotch strap adjustability: Yes
  CR bight to nearest crotch strap position: 9.5 in./24 cm (using minimum seat depth adjustment plus an additional 2.7 inch strap adjustment offered in that setting.)
  CR bight to farthest crotch strap position: 15 in./38 cm


  Semi-recline allowed in forward-facing position: Yes; backrest adjusts to match vehicle seat


  Tether present: No
  Special tethering: n/a

Accessories / Add-ons

Standard accessories:

  • Swivel base with lock-out function and up to 10° tilt option
  • Shoulder pads
  • Crotch pad
  • Mounting options for add-on accessories
  • Removable, machine-washable cover

Add-on accessories:

  • Chest clip
  • Leveling and protection cushion
  • Front stand (with or without footrest)
  • Belt guide (to equip seat with guides on both sides)
  • Height-adjustable head rest
  • Lateral trunk supports (fixed or swing-away)
  • Upper body guides (fixed or swing-away)
  • Abduction block
  • Leg guides

Miscellaneous Information

  • MSRP (U.S. dollars): Starts at $3,580.00
  • Company certifies to meet standard:
    • FMVSS213 (U.S.): Yes
    • CMVSS 213 (Canadian): No
  • Will ship to Canada? No
  • Owner’s manual languages available: English

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