<p>A gas supply pipe is provided with a distributor based on a porous diffuser element. The diffuser element is mounted on a plate with a central connector which fits into an opening in the gas pipe. A threaded fixing stud is used to secure the whole assembly. - The connector and the fixing stud are located by shoulders. The fixing stud is provided with an inner passage which connects the gas pipe to the space between the support plate and the diffuser element</p>
