A request for a large ring is hard to price if it gives only the outside diameter. The supplier needs to know the size, the duty and the date.
Send a drawing if one exists. If not, give the groove diameter, width and depth, whether the gland is a face or radial seal, and any sound measurements of the old ring. Say clearly whether a quoted diameter is internal or external. Include the quantity, site and latest useful delivery date.
Then give the fluid and concentration, normal and peak temperature, pressure or vacuum, any relative movement, and the cleaning cycle. Name any required material approval or traceability. If a joint is acceptable only as an interim repair, say so. A photograph of the joint area and the flange can help the supplier spot an installation issue.
Ask the quote to state the construction, for example compression step moulded CO.SM.O, and the chosen compound. Name any approval the duty needs. Approvals such as FDA, 3-A, USP and Norsok are available but not universal, so confirm the approval against the exact compound offered. Ask for the quoted tolerance and inspection grade, and a confirmed UK delivery date. That gives engineering and purchasing the same specification to review. It also makes a later repeat order less dependent on memory.
Related: large diameter O rings, getting a large O ring when no standard size fits, large O ring supply for a shutdown, specifying large O ring tolerance and the guides library.