This late Commonwealth period cover I certify as a super postal history piece and hats off to the buyer and under bidder for recognizing this. Somewhat looking ordinary, the 4c franking is EXTREMELY SCARCE ON COVER, both for domestic and outbound mail. The4c value was explicitly issued for the single outbound circular rate could could also be used for double domestic first class rate, which is also extremely scarce on cover. There reason for this was the over abundance of the 2c Rizal which was used on multiple rated official mail. (eBay $127.00)

To date I have seen, excluding the above, three covers with the above franking all from the Philippine Education Company (PECO). It seems that PECO was one of the very companies that really availed of the outbound circular rate.

The 1939 Postal Regulations on 3rd Class Mail matter as follows:

THIRD-CLASS.— Third Class matter embraces circulars, Books (Including Catalogues)
having, including the covers 24 pages or more, arid other printed "matter on paper not
having the nature of an actual personal correspondence (except newspapers and periodicals admitted to the second class), proof sheets, corrected proof sheets and manuscript copy accompanying the same, matter in point print or raised characters used by the blind, drawings, merchandise, seeds, bulbs, cuttings, roots, scions, and plants, and all other mailable matter not embraced in the first and second classes when sent in packages weighing up to and including 220 grams. The same matter when sent in parcels exceeding 220 grams in weight is embraced in fourth class or parcel post mail.

POSTAL RATE: 4 centavos for each 55 grams or fraction, up to and  including 220 grams   in weight, except that books, catalogs, seeds, cuttings, bulbs, roots, scions, and plants, not exceeding 220 grams in weight is 2 centavos for every 55 grams or fraction thereof,  on, each individually  addressed piece or package. The  2-centavo rate does not apply to  blank books or to those mainly blank.