At MANN+HUMMEL’s IAM Customer Service Centre in Ludwigsburg, expert staff have the task of responding to queries from our independent aftermarket customers around the world. Every now and again we also receive handwritten letters or letters typed on typewriters. These usually come from individuals or long-standing agricultural holdings. Take the following case of the owner of a small electric works in Mallersdorf-Pfaffenberg, Lower Bavaria, who contacted us with the following request.

The owner of the electric works needed a replacement for an OPM 90/40 E-20-type MANN strainer disk filter, which the company had bought from FILTERWERK MANN & HUMMEL GMBH more than 60 years earlier. Enclosed with the hand-typed letter was order confirmation no 6544 dated 15/12/1953, addressed to:

Mallersdorf Abbey

Electric works

Mallersdorf, Lower Bavaria

One of the words in the address may be puzzling you at this point. To explain, the small electric works in Mallersdorf-Pfaffenberg was owned for many years by the Mallersdorf Benedictine Abbey that once was, before being bought by a private owner a few years back, who then wanted to update the technical equipment and ensure good working order. One of their servicing tasks was to replace the above-mentioned old strainer disk filter, which had been delivered and installed at the end of 1953. It’s fair to say that, after 60 years and countless operating hours, the MANN-FILTER product had reached the end of its service life.

The ‘1975 conversion list to Hollerith numbers’

The religious people at the Abbey probably realised at the time that order confirmation no 6544 would help again one day when it came to obtaining spare parts – they stored it in their archives for decades after all. Using our ‘1975 conversion list to Hollerith numbers’, we were able to recode the old OPM 90/40 E-20 type of filter to a valid ten-digit part number – 61 504 53 101. The new owner of the electric works received a drawing of the new filter from us, as well as information about the delivery time and a list of delivery options.


Are you still wondering about the ‘1975 conversion list to Hollerith numbers’ though? To explain, in the 1950s, MANN-FILTER order numbers (e.g. for our strainer disk filter) consisted of a combination of letters and numbers. At the start of the 1970s, MANN+HUMMEL introduced the ‘Hollerith’ numbers, which had ten digits and used numbers only. The name ‘Hollerith’ comes from the one-time punch card method used in IT, which was invented by US engineer Herman Hollerith (1860–1929) and had been used in many companies, including MANN+HUMMEL. After this method was introduced, the old combinations of letters and numbers were converted to ten-digit Hollerith numbers, which are still the ten-digit part numbers in use today.

Exquisite choice of words

One more thing that caught my eye on the order confirmation from 1953 was the letterhead, which had our first-ever MANN-FILTER logo printed on it. At that time, the MANN+HUMMEL company name was still being linked with an ‘&’. This was of course replaced by a ‘+’ later. The wording used in the old text, typed on to the confirmation by our colleagues back in the day, also struck me: “We make every effort to process your order with the utmost care and are at your service.” Even in those days, enormous importance was attached to great customer service – in the 1950s, our letters would commonly end with ‘Respectfully yours’! The format and layout of business correspondence have changed radically since 1953, but our constant drive for excellent customer service and satisfaction has not.