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Frequently Asked Question

 
Below are some of the most frequently asked questions. If you cannot find the answer to your question here, please feel free to contact Rollfast.
 
 
Why is stainless steel "stainless"?
 
Stainless steels are iron alloys with a minimum of 10.5% chromium with other elements (Nickel, Molybdenum, Titanium, Copper, Carbon, Nitrogen) added to enhance properties such as formability and strength. But it is the chromium-rich, oxide film that gives the corrosion resistance of stainless steel. This protective film is strong and chemically stable (i.e. passive) where there is sufficient oxygen on the surface. This strong protective film is extremely thin and will usually self repair if sufficient oxygen available. Under certain conditions the passive state can be broken down and corrosion can result. Therefore the correct grade must be selected.
 
 
Should I buy A2 (304) or A4 (316) stainless steel fastenings?
 
A2 and A4 are known as Austenitic grade of stainless steel with the A4 grade having a higher corrosion resistance than A2. They are both non-magnetic.

Grade A2 (AISI 304) has excellent resistance to atmospheric corrosion, except in severe industrial and marine environments. 
Typical applications include street furniture, food processing, domestic appliances, medical and brewing equipment, fasteners for aluminium alloy, plastics, building fixings and fastenings for oak. Also suitable for most non-saltwater marine domestic applications.

Grade A4 (AISI 316) has a higher corrosion resistance than A2 grade in many chemical environments, including contact with dilute sulphuric acid, and acetic acid. Suitable for marine conditions, but not recommended for immersion in sea water.
Typical applications include fasteners for boat deck fittings, chemical plants, swimming pools, dye vats, sewage treatment plants, dairy and medical sterilising equipment, and specialist building fixings.
 
 
Is stainless steel environmentally friendly?
 
Recycled scrap is used to produce over 90% of new stainless steel, and all stainless steel is fully "recyclable" at the end of its useful life. Great care is taken to minimise fume and dust emissions in the production of stainless steel. The steel is melted electrically and in most cases refined by using inert air distilled gases, such as argon. Life expectancy in stainless steels is usually long because of there corrosion resistant quality. Only minimum maintenance is needed therefore eliminating the environmental problems and costs of painting or galvanizing. Stainless steel is easy to clean and safe, being widely used for catering equipment and food manufacturing.
 
 
Why are there rusty marks on my stainless steel?
 
These rusty marks are unlikely to be the result of corrosion to the stainless steel, but are likely to result from small particles of "ordinary" (non-stainless) steel from wire wool or scouring pads becoming attached or embedded in the surface. In the damp environment these iron particles rust and cause staining. Rust marks may be removed using non-scratching creams, or an oxalic acid solution, where iron particles have been embedded in the surface. Special precautions should be taken with oxalic acid, as if ingested is poisonous
 
 
What does the 70 or 80 in a stainless steel bolt head mean?
 
The 70 or 80 refers to the tensile strength of the bolt; this is the maximum stretching force it can withstand before breaking. The class 80 bolt is stronger than the class 70. Class 70 is the most commonly used type of fastener. 

The tensile strength of class 70 bolts =<M24 is 700Nmm2 , while class 80 bolts =<M24 is 800Nmm2. 
   
  How do I convert Imperial sizes to Metric?
 
INCHES METRIC
Fraction 1/1000th " mm
1/64 0.016 0.40
1/32 0.031 0.79
  0.039 1.00
3/64 0.047 1.19
1/16 0.063 1.59
5/64 0.078 1.98
  0.079 2.00
3/32 0.094 2.38
7/64 0.109 2.78
  0.118 3.00
1/8 0.125 3.18
9/64 0.141 3.57
5/32 0.156 3.97
  0.157 4.00
11/64 0.172 4.37
3/16 0.188 4.76
  0.197 5.00
13/64 0.203 5.16
7/32 0.219 5.56
15/64 0.234 5.95
  0.236 6.00
1/4 0.250 6.35
17/64 0.266 6.75
  0.276 7.00
9/32 0.281 7.14
19/64 0.297 7.54
5/16 0.313 7.94
  0.315 8.00
21/64 0.328 8.33
11/32 0.344 8.73
INCHES METRIC
Fraction 1/1000th " mm
  0.354 9.00
23/64 0.359 9.13
3/8 0.375 9.53
25/64 0.391 9.92
  0.394 10.00
13/32 0.406 10.32
27/64 0.422 10.72
  0.433 11.00
7/16 0.438 11.11
29/64 0.453 11.51
15/32 0.469 11.91
0.472 12.00
31/64 0.484 12.30
1/2 0.500 12.7
0.512 13.00
33/64 0.516 13.10
17/32 0.531 13.49
35/64 0.547 13.89
0.551 14.00
9/16 0.563 14.29
37/64 0.578 14.68
0.591 15.00
19/32 0.594 15.08
39/64 0.609 15.48
5/8 0.625 15.88
  0.630 16.00
41/64 0.641 16.27
21/32 0.656 16.67
0.669 17.00
43/64 0.672 17.07
INCHES METRIC
Fraction 1/1000th " mm
11/16 0.688 17.46
45/64 0.703 17.86
  0.709 18.00
23/32 0.719 18.26
47/64 0.734 18.65
  0.748 19.00
3/4 0.750 19.05
49/64 0.766 19.45
25/32 0.781 19.84
  0.787 20.00
51/64 0.797 20.24
13/16 0.813 20.64
  0.827 21.00
53/64 0.828 21.03
27/32 0.844 21.43
55/64 0.859 21.83
  0.866 22.00
7/8 0.875 22.23
57/64 0.891 22.62
  0.906 23.00
29/32 0.906 23.03
59/64 0.922 23.42
15/16 0.938 23.81
  0.945 24.00
61/64 0.953 24.21
31/32 0.969 24.61
63/64 0.984 25.00
1 1.000 25.40
     
     
   
  How do I convert a Screw No to a Metric size?
 
WOOD SCREW
GAUGE
METRIC
EQUIVELENT
IMPERIAL SCREW
LENGTHS
METRIC
EQUIVELENT
No mm No mm
No4 (2.9mm) 3 3/8 (9.5mm) 10
No6 (3.5mm) 3.5 1/2 (13mm) 12
No8 (4.2mm) 4 5/8 (16mm) 16
4.5 3/4 (19mm) 20
No10 (4.8mm) 5 7/8 (22mm)  
No12 (5.5mm) 5.5 1 (25mm) 25
No14 (6.3mm) 1 1/4 (32mm) 30
    35
    1 1/2 (38mm) 40
    1 3/4 (45mm) 45
    2 (50mm) 50
    2 3/8 (60mm 60
    2 3/4 (70mm) 70
   
   
 
 
 
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