On 14 August 2013 17:03, YES NOPE9 wrote: > I had the motivation to look up some mechanical specifications for the > connectors used in landline telephones and for the connectors used with > CAT5 ethernet cable. > > I was surprised to learn the contact spacing was 1.02 mm ( .04 in ) for > RJ-11 , RJ-45 , RJ-9 , RJ22 , RJ-10 , RJ-25 , RJ-14 > Is this correct ? And why did they choose 1.02 mm ? I see they were > patented in 1975. 1975 sounds very late in the game. Short: 25.4 mm/25 =3D 1.016 mm ~+ 1.02mm Longer: They will be imperial measurement specified, with subsequent conversion to mm 1 foot =3D 0.3048 metre EXACTLY by international agreement. So one inch =3D 0.3048/12 =3D 0.0254m =3D 25.4mm EXACTLY. Space connectors at 1/25th of an inch and spacing =3D 25.4/25 =3D 1.016mm ~= =3D 1.02mm Error is +0.39(3700787)%. Over an 8 pin CAT5 connector with 7 spaces the error is +0.39*7 =3D 2.73% (= or 2.76% if you don't use shonky rounding :-) ie in this case the difference between using imperial and metric or metric approximations of imperial would possibly not stopp you landing successfully on Mars. Russell --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .