There are a vast array of different stainless steel types which can cause a lot of confusion.

The most popular grades are :

1. A2 (or 304) Stainless -  resistant to corrosion  
2. A4 (or 316) Stainless -  higher degree of corrosion resistance

Generally - pick A4 grade if parts are used in any marine environment or, on land but close to the sea.

For Specific information on all the different grades available and further information on suitability of use/welding etc see :

The technical library of the British stainless steel association:

Here you will find further categories such as Corrosion & Oxidisation :