Pat, I see no reason that the drives can not be called as 6.5 mm, 9.5 mm and 12.5 mm to replace the 1/4, 3/8 and 1/2 name. Even if they are made to the metric equivalent of those dimensions I doubt there would be any notice. 9.5 mm and 3/8 are the same thing. 12.5 mm is 0.2 mm shorter then 12.7 mm and no body is going to tell me that 0.2 mm smaller drive is going to cause the socket to fit loose. I'm sure that with tolerances considered both would work. 6.5 mm is 0.15 mm larger and may present a problem, but I'm not sure. A slightly bigger post may not fit an existing socket. It all depends on the tolerances allowed. Even if it is made to 6.35 mm, it can still be called a 6.5 mm for simplicity.
A perfect example of this is phone jacks. There is the old 1/8 inch that was some time ago changed to a 3.5 mm. In fact for some time in advertising the names were often interchanged. Yet, 1/8 inch is 3.175 mm, a difference of 0.325 mm, which is a much bigger difference then 1/4 inch and 6.5 mm. So what is it really? Was it 1/8 inch at one time and then changed to 3.5 mm or is it 3.2 mm and just called 3.5 mm? Check out this web site and you will see that phone jacks are called out in millimeters only: http://www.tradekey.com/product_view/id/755502.htm Here is a PDF with technical drawings. Starting on page 5 are the technical drawings: http://www.shokaifareast.com/images/Connectors/3.5MM%20Jacks/3.5MM_Jacks_red.pdf It looks like the sleeve is a true 3.5 mm +/- 0.05 mm. The mating holes on the female part are 3.6 mm, only 0.1 mm larger. However it does look like the 1/4 inch style is made to 6.34 mm (not 6.35 mm an thus is not a true 1/4 inch) +/- 0.01 mm from this page: http://www.shokaifareast.com/images/Connectors/6.4MM%20Jacks/6.3MM%20Jacks%20Low%20Res.pdf It shows with proof that an inch based part is really made in metric. As with tires, I see no reason the designations can't be stated in increments of 25 mm and still be within tolerance: I believe these are the most common sizes: 13 inch = 330 mm 14 inch = 355 mm 15 inch = 380 mm 16 inch = 405 mm 17 inch = 430 mm I see no reason why a P195R75-15 tire can not be called a P195R75-380. At least this way all the numbers are in the same units. Simplicity and consistency. Do you agree? Monitors don't use DPI, they use millimeter pitch. Printers can do the same. At lease this way resolution in print canbe compared to resolution on the screen. So much for monitors being inch based with a metric dot pitch. In many cases it doesn't matter to us if the part is made to a soft converted number ot a slightly modified soft conversion (12.7 mm becoming 12.5 mm) as long as it is designated by a hard converted metric reference. The anti-metrics like to keep the old designations so that they can claim English units are still used, even if deep inside they know the parts long ago went to metric dimensioning. Obsolescence of old inch based parts can actually solve the issue the best. Jerry ________________________________ From: Pat Naughtin <[email protected]> To: U.S. Metric Association <[email protected]> Sent: Saturday, March 14, 2009 4:11:55 PM Subject: [USMA:43848] Soft conversion always fails Dear All, Recently, although it was not mentioned by name, there has been a lot of discussion about the efficiency of soft conversion during a metric transition. Examples were: *Listing the drive shaft on a socket spanner as 1/2" — instead of the true design dimension and the true make dimension of 12.7 millimetres. This is a sure way to continue the discussion about the metric vs old pre-metric measures question for 100 years or more. Good metrication plans have statements like: 'If parts have to be chosen to match old heritage standards, then the part will be specified in the equivalent metric units — the name of the old pre-metric measure should not be mentioned ever again. It should not be used in any calculation and it should never be written down. Here are some examples of soft conversions that have been discussed on this list: *Tyre (tire) sizes are designed and measured during manufacture using metric sizes (e.g a wheel is designed rim is measured as 356 millimetres to meet an old pre-metric specification of 14 (1959 metric) inches) then that size should be specified in metric units to the nearest whole number of millimetres; in this example as 356 mm. It's bad enough having to accommodate heritage measures without also having the problem of generating heritage disputes as well. *Although print definition is mostly hidden by never mentioning any units at all, the recurrence of dpi gives credibility to a measure that is rarely used or recognised. This might be a great opportunity to reconsider the whole issue of image definition pixels, and the way these are measured and calculated. *Nominal pipe sizes are now, and always have been, based on absolute lies. They were either intended to deceive or, if they happened by accident, it has been continued for decades for deceptive purposes. It is a completely irrelevant topic and there should be no need for anyone in the world to ever consider such nonsense, For example, the use of nominal pipe sizes does not conform to American Standard pipe designations. See http://www.engineeringtoolbox.com/nps-nominal-pipe-sizes-d_45.html to find out about real, current, and relevant world standards using millimetres. *Some automotive parts (such as a front disc brake rotor) suffered from a 'soft conversion' in the 1970s when (say) an 11 inch disc became a 280 millimetre during the worldwide metric transition in the automotive industry that was known as developing the 'world car' concept in the 1970s. Soft conversions are always subject to pressure to reversion for as long as they can be recognised as soft conversions. I shudder to think of the cost of all the discussion that soft conversion generates through constant recalculation of the old equivalent pre-metric measure, the correction of the mistakes converting to the old measure, and the constant discussion about generated questions like: Why don't we finish the metrication? or This is silly why don't we go back to the old days? Maybe I should raise the estimate of how much it costs the USA not to go metric; see http://www.metricationmatters.com/docs/CostOfNonMetrication.pdf ! However, some government agencies go soft on soft conversions, such as the U.S. Department of Transportation Federal Highway Administration at http://www.tfhrc.gov/pubrds/summer95/p95su14.htm (see 1995 quote below). Perhaps they have not had enough experience with the metrication process to know that soft conversions almost always fail. Hiding soft conversions with consistently applied metric specification helps a little, but soft conversions are best avoided altogether or only ever used as a stop gap to give you time to rethink the old sizes and to use the opportunity of the metrication process to redesign, to rationalise wastes and to reduce costs. "Hard" Versus "Soft" ConversionThe federal government makes a distinction between "hard" and "soft" conversions to the metric system. A soft conversion is a direct mathematical conversion from a U.S. measurement to its metric equivalent e.g., from 180 pounds to 81.65 kilograms. A hard conversion is the creation of a new, rounded, rationalized number that is easy to work with and easy to remember. FHWA encourages the use of hard conversion as much as practicable. Where hard conversions have not been established, however, state highway agencies should use soft conversions. The bottom line is that a project should not be delayed simply because some hard conversions have not been developed yet. Several agencies, including FHWA, have adopted the American Society for Testing and Materials (ASTM) manual E380 as the standard for making metric conversions. An excellent reference is the Metric Guide for Federal Construction published by the National Institute of Building Sciences. By the way, in the next paragraph, the U.S. Department of Transportation Federal Highway Administration makes it absolutely clear that they believe that the way forward to metrication is through encouraging as much metric conversion as they can. Efforts are not standing still between conferences. The ideas generated in conference are being put into action. Other FHWA metric training and education efforts include the following: 1. FHWA has developed and distributed more than 150,000 metric/U.S. measurement conversion slide rules to its field offices, state highway agencies, technology transfer centers, and other appropriate offices. 2. Two of FHWA's regional offices have developed computer conversion programs for general use. These programs have been distributed agencywide and are available on FHWA's electronic bulletin board. 3. FHWA developed and has made available a computer software program that can be used within WordPerfect to convert U.S. measurement units to metric units. 4. FHWA has developed and made available a metric poster and a metric cube (a small box with metric conversion information on all six sides). As most of you know, I consider the metric conversion process to be so slow, socially painful, and expensive that I would never recommend it to any organisation. See http://www.metricationmatters.com/metric_conversion.html and also http://www.metricationmatters.com/docs/ApproachesToMetrication.pdf where I rate metric conversion little higher that ignoring the whole process and hoping it will go away! Cheers, Pat Naughtin PO Box 305 Belmont 3216, Geelong, Australia Phone: 61 3 5241 2008 Metric system consultant, writer, and speaker, Pat Naughtin, has helped thousands of people and hundreds of companies upgrade to the modern metric system smoothly, quickly, and so economically that they now save thousands each year when buying, processing, or selling for their businesses. Pat provides services and resources for many different trades, crafts, and professions for commercial, industrial and government metrication leaders in Asia, Europe, and in the USA. Pat's clients include the Australian Government, Google, NASA, NIST, and the metric associations of Canada, the UK, and the USA. See http://www.metricationmatters.com/ or to get the free 'Metrication matters' newsletter go to: http://www.metricationmatters.com/newsletter to subscribe.
