Hole Reinforcement for Composites

FTI's patented GromEx system is a cost-effective method for reinforcing fastener holes in composite materials using a thin interference fit metal sleeve or grommet. GromEx is based on FTI's proven cold expansion technology and is designed specifically for use in composites.

The amount of radial expansion of the grommet in the hole is carefully tailored to ensure adequate grommet retention and at the same time prevent localized damage to the composite. The GromEx system is easier to install, more reliable, and has improved performance over adhesive bonded or swaged grommets.

FTI expanded products achieve excellent bonding and grounding (or earthing) performance because each product is radially expanded from a clearance fit starting hole to produce a final interference fit in the structure or component. Our highly repeatable process produces uniform contact with the hole surface without gaps or insulating sealant. GromEx panel liners are used to protect composite panels from lightning strike damage and hole wear. They are suitable for use with any class or fit fastener and can be used to facilitate the installation of net fit fastners in load transfer applications. GromEx is available in common fastener configurations including "t-shape" and 100 degree countersunk configurations.

Benefits of GromEx

• Initial clearance fit of grommet:
  • Ease of installation
  • Prevents installation damage


• Installation without adhesives or sealants:
  • Significant installation labor savings
  • Reliable, better process control
  • No messy compounds or cure procedures
  • Assured grommet concentricity in hole


• Quality installation:
  • Consistent fit
  • Can be used in a wide range of composites


• Improved damage tolerance:
  • No fastener installation and removal damage
  • Better galvanic compatibility
  • Enhanced resistance to lightning strike damage
  • Protects the hole geometry under compressive loads

• Carbon/epoxy, carbon/BMI, Carbon/polyamide


• Aramid/epoxy


• Glass/epoxy


• 2D cross-laminated tape and fabric laminates, & short fiber


• 3D products

• Commercially pure titanium


• Passivated austenitic stainless steel


• Countersunk (100°), 0.010 inch nominal wall thickness. Fastener may be installed interference or clearance fit to NAS618 standards through use of appropriate tool set and starting hole. Thicker walled grommets available.

• Standard system: From 3/16 to 1/2 inch in 1/16 inch increments