Plate Welding Thickness

These are terms from shop language.

Not conforming to any standard.

Light will be upto 3mm thick,Med will be upto 10mm and Heavy above 12mm

While on the subject it is better to think about Root gaps kept deliberately -both for fillet welds and for the once-through pass:

http://www.aws.org/cgi-bin/mwf/topic_show.pl?tid=13851 gives some thoughts.

As my friend MM has suggested , the terms mentioned by you are of shop language for fillet welds.

To add further to what he has said, any butt joint up to 10 to12 mm thickness plate will have a reinforcement of 1.5 mm with tolerance of 0.5 mm on higher or lower side. beyond that , it could be up to 2 to 3 mm as it is not practical to control the build up to close tolerances and heavy build up will not contribute towards its joint strength and lower build up will not carry the required load.

For fillet welds, the minimum leg length could be 3 mm or so and for any load bearing structure, the leg is designed to have a weld equal to 0.75 times the thickness of plate used. For non load bearing it could be 0.38 of the thickness used.

Hence there is no such light, medium, or heavy weld-ments. It all depends upon the thickness of the plates used.