Plas-Fix 45 Screws Installation Guide

This article provides installation assitance for the Metric Plas-Tech 45 threadforming screws.

Design

 
Plas Fix 45

The Plas-Fix 45 is a trilobular bodied, high performance Metric thread forming screw for plastics available with a Supadrive® and Torx® recess drives and Countersunk and Pan head styles as standard.  

A wide variety of plastics are now available in the market place. These vary considerably in their hardness, susceptibility to cracking and stability to temperature and humidity variations. 

 

When specifying a fastener for plastics, the following guidelines should be considered:     

  • Chamfer all pilot holes to the screw major diameter to eliminate cracking    
  • Boss heights should be designed so that there is no clearance between the top of the boss and the component being clamped.    
  • Boss diameters should be 2.5 - 3 times the pilot hole diameter.    
  • The ratio of stripping torque to tapping torque should be at least 2-1 (3-1 being ideal)   
  • Pilot holes should provide for a minimum thread engagement of 2 times the screw diameter.    
  • The pilot hole should be determined by application testing relative to the assembly requirements  
  • Specific application tests should be carried out if there is any doubt about suitability.
     

Tightening    

Ideally, the thread stripping torque for the application should not be in excess of the minimum torsional steength of the screw, thus ensuring that the full potential of the screw is achieved. Under these conditions a tightening torque of 75/80% of the minimum torsional strength of the screw is recommended.  

For applications where the thread stripping torque achieved is less than the minimum torsional strength of the screw, ie in soft plastic materials or where thread engagement is restricted to a minimum, the recommended tightening torque should be set at 75/85% of this thread stripping torque.  

As a general guide, tapping torques should be in the region of 33% of the thread stripping torque.  

In most cases it is a matter of balancing one factor against another to obtain optimum results. 

It is always adviseable to conduct tests on proposed applications before they are implimented. 

Boss Geometry

 

The following table illustrates the guideline hole sizes.

Screw Size Thread Eng't ABS Nylon 6 Nylon 66 Nylon 6 GRP Polypropylene Polyethylene Polyphenylene Oxide GRP
Hole Dia Drill Size Hole Dia Drill Size Hole Dia Drill Size Hole Dia Drill Size Hole Dia Drill Size Hole Dia Drill Size Hole Dia Drill Size
M2.5 x 1.4 4 1.8 1.8 1.85 1.8 1.8 1.8 2.0 2.0 1.85 1.8 1.8 1.8 1.85 1.8
6 1.9 1.9 2.0 2.0 2.1 2.1 2.1 2.1 1.9 1.9 1.85 1.8 2.1 2.1
9 2.1 2.1 2.0 2.0 2.1 2.1 2.1 2.1 2.1 2.1 1.85 1.8 2.1 2.1
M3 x 1.5 5 2.25 2.2 2.3 2.3 2. 2.3 2.3 2.3 2.2 2.2 2.25 2.2 2.25 2.2
8 2.37 2.4 2.3 2.3 2.37 2.4 2.37 2.4 2.2 2.2 2.25 2.2 2.45 2.4
11 2.37 2.4 2.37 2.4 2.45 2.4 2.56 2.6 2.4 2.4 2.3 2.3 2.56 2.6
M3.5 x 1.65 5 2.7 2.7 2.75 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.75 2.7
9 2.7 2.7 2.8 2.8 2.8 2.8 2.75 2.7 2.7 2.7 2.75 2.7 2.75 2.7
13 2.9 2.9 2.9 2.9 2.9 2.9 2.9 2.9 2.8 2.8 2.75 2.7 3.05 3.0
M4 x 1.75 6 3.1 3.1 3.2 3.2 3.1 3.1 3.2 3.2 3.2 3.2 3.1 3.1 3.1 3.1
10 3.1 3.1 3.3 3.3 3.4 3.4 3.3 3.3 3.2 3.2 3.1 3.1 3.4 3.4
14 3.4 3.4 3.4 3.4 3.5 3.5 3.5 3.5 3.3 3.3 3.1 3.1 3.5 3.5
M5 x 2.2 8 3.4 3.4 3.6 3.6 3.6 3.6 3.4 3.4 3.6 3.6 3.4 3.4 3.6 3.6
13 3.6 3.6 3.8 3.8 4.0 4.0 4.1 4.1 3.6 3.6 3.4 3.4 4.0 4.0
18 4.1 4.1 4.1 4.1 4.1 4.1 4.1 4.1 3.8 3.8 3.4 3.4 4.0 4.0
M6 x 2.5 9 4.5 4.5 4.5 4.5 4.85 4.8 5.2 5.2 4.7 4.7 4.5 4.5 4.85 4.8
15 4.7 4.7 5.0 5.0 5.2 5.2 5.2 5.2 5.0 5.0 4.5 4.5 5.0 5.0
21 4.85 4.8 5.2 5.0 5.2 5.2 5.2 5.2 5.0 5.0 4.5 4.5 5.2 5.2
Note: Due to the fact that fastening applications differ greatly, the above information is for guidance only and is correct to the best of our knowledge. The customer must satisfy themselves with the performance of the fastener and validity of the data. TR Fastenings will not be held responsible for any failure that may occur from the use of this information.