Contractors Unlimited

Technical Toolbox

As a contractor, you are only as good as your last job. So being able to find information quickly and easily is an important skill. The following list of engineering resources in the form of charts, tables, graphs, definitions and links will hopefully make life easier. If you would like to see a particular topic added to the toolbox then let us know - select the link at the bottom of the page.

ASCII Character Table

The basic ASCII Character Table for numbers 0 to 127.


EU directive 94/9/EC, compliance and equipment markings.

Cable Glands

The selection and sizing of cable glands.

CE Marking

CE Marks and their application.


Control of Substances Hazardous to Health Regulations 2002.

Electric Motors

Formulas relating to electric motors

Electronic Wire and Cable

Stranding, diameters & areas of copper electronic wire & cable.


Glossary of General Engineering Terms and Acronyms
Glossary of Nuclear Terms and Acronyms

Hazardous Areas

Classification of hazardous areas and comparison of standards


HAZID studies and HAZID study guide words


HAZOP studies and HAZOP study guide words

Hot Bolting

The practice of removing and replacing or freeing and re-tightening bolts on live piping and equipment


Hydraulic Fluid Cleanliness - use of current standards
Comparison of ISO and NAS cleanliness classes


Rough guide to the meaning of the 13 Incoterms.

Ingress Protection Ratings

IP Codes, and comparisons with NEMA system.

Machineability of Materials

Points to Note When Cutting.

Pipe Flanges

Pipe flange dimensions for common sizes and ratings.
Common terms for surface roughness of flange mating faces.

Pipe Schedules

Pipe schedules, wall thickness and weights.

Polarisation Index of Electric Windings

Use of Polarization Index for AC & DC drives and generators.

Power Factor Correction

Power Factor definition, calculation and correction techniques.

Pressure Gauges

Selection, installation & use of Bourdon tube pressure gauges.

Pump Affinity Laws

Affects of changing pump speed on flow rate, head and power.

Relief Valve Orifice Sizes

API standard Relief Valve Orifice Sizes

SI Units

The 7 base units and the derived units defined and explained.
Form decimal multiples and submultiples of SI units.

Safety Integrity Ratings

SIL Ratings and how to determine them.

Stainless Steels

Grades of stainless steels, their compositions and properties.

Straight Length Requirements

Straight Lengths needed & installation notes for Vortex Flow meters

Stud and Nut Sizes

Stud diameters & corresponding nut sizes in metric & imperial.

Temperature Classification

Temp class for hazardous area products - European & US

Thermocouple Types

Standard combinations of metals and their measuring ranges

Unit Conversions

On line conversion between all units of temperature.

Valve Leakage

Valve leakage classes and testing explained.


Limits to the location of nozzles on vessels.


Definitions, units and conversions.

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