CELO, global industrial fasteners and screw manufacturer

Boss design for REMFORM® II HS™

In order to ensure a safe installation and stable clamping force, it is relevant to pay attention to the boss design, as it must resist mold extraction and cooling tension as well as tension created during screw installation.

It’s important to include a relief bore to prevent damaging the boss when starting thread forming. The relief bore also helps to align the screw during threading.

The dimensions for external diameter, core hole diameter and minimum depth will vary based on the type of plastic.

boss dimensions REMFORM II HS

For softer plastics not listed above, use Øa = 0.75 x d and other parameters as detailed for PC.








d = screw diameter

Øa = core hole diameter

Øext = external diameter




Length of engagement Le = 2.3 x d

Minimum depth P = 2.9 x d

Relief bore height T = 0.25 - 0.5 x d

Relief bore external diameter Øb = 1.05 - 1.1 x d




*For PC:

Length of engagement Le = 2 x d

Minimum depth P = 2.7 x d

boss design recomendation

Suggested tolerances:

+0.08 mm for holes ≤ Ø3.0 mm

+0.10 mm for holes Ø3.0 - Ø4.5 mm

+0.12 mm for holes > Ø4.5 mm

This data is intended for guidance purposes. We recommend carrying out relevant tests on plastic parts to establish the precise values.

Assembly recommendations


Assembly recomended plastic torque

Tr = Threading torque

Ta = Tightening torque

Tf = Failure torque


For additional information about the boss design for direct assembly in plastic parts, please contact our technical department.

Published: 2021-04-08