Within a technical specification you should avoid references which may unduly favour or eliminate suppliers e.g. by asking for a specific material or goods.  

You should not reference a specific make or source or to a particular process, trademark, patent, type, origin or means of production.

Examples

Do not specify "Hoover" when you mean a vacuum cleaner or "Intel" when you mean a central processing unit of a personal computer.

In exceptional circumstances such mention may be justified if:

• the contract's subject makes using it unavoidable or
• the contract's subject cannot be described in any other way that is precise and able to be understood by all potential bidders.

In either of the above circumstances such mentions should be accompanied by the words "or equivalent".