1. Use of API 6A vs ISO 10423 in marking 6A equipment

2. Issues
ISO th Edition requires marking to include “ISO 10423” and does not make any allowance for using API 6A as an alternative.
The allowance to use API 6A is not included in the regional annex as it was in the 19th Edition.
The use of API 6A is only discussed in Annex P which is an informative annex for use of API monogram and could imply it only allows use of 6A on monogrammed equipment.

3. Background Use of spec number in making occurs in several places.
8.1.1 – General
Equipment shall be marked on the exterior surface as specified in Table 39. Marking shall contain the designation ISO 10423, the temperature classification, or maximum and minimum operating temperatures, material class, product specification level, performance requirement level, date of manufacture (month and year), and manufacturer's name or mark. Other marking shall be as specified in Tables 39 to 47. Marking for features that do not exist on a product is not applicable.
Table 39
8.1.9 – Hubs (requires marking ISO 13533)
8.2 – Wellhead equipment
8.5(e&f) – Safety Valves
VR Plugs
8.11 – Bullplugs
8.12 Back-pressure valves
H.5 – Running Tools
L.7 – VR Plugs

4. What has been done in other ISO/ API standards?
ISO13533/ API Spec 16A
Equipment shall be stamped on the product with the product description code (PDC) or alphanumeric code, followed by “ISO 13533” or "API 16A".
ISO 14313/API Spec 6D
For identical national adoptions of this International Standard, other nationally recognized designations may be marked in addition to those given in ISO 14313, e.g. ISO 14313/API Spec 6D.
ISO 11960/ API Spec 5CT
Specifically states that it is an option to stamp either API 5CT or ISO 11960
ISO / API Spec 7-1
Allows for API 7-1 in an addendum

5. Recommendations
Add clause from 19th Edition Regional Annex into 20th Edition Regional Annex
“Manufacturers shall mark their equipment with ‘API 6A’ in addition to or in place of ‘ISO 10423’ in the location specified in this clause. As a minimum, equipment should be marked with US Customary Units.”
Add one of the following to 20th Edition regional annex
Replace clause 8.1.9(b) with either;
“Hub end connectors shall be marked "ISO or API 16A" following the size and pressure rating. Or
“Hub end connectors shall be marked in accordance with ISO