Hello everybody, I've never worked before in imperial dimension,

please what is mean this sizes over red line? please see attached file.

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3 Answers

The "Drill No. 38" is designating a drill size that is common in the U.S. #38 is equal to .1015 decimal inches. Here is a link to a chart:

http://www.gearhob.com/eng/design/drill_eng.htm

The other item "TAP 3-48" is a reference to how tapped holes are typically called out. in this caase the 3 is specifying a particulat size dia. (.099 decimal inches) and the 48 specifies the threads per inch. Here is a link:

http://www.carbidedepot.com/formulas-tap-standard.htm

 
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The note DRILL No38 refers to the size of bit that should be used to drill the hole. Google drill and tap chart - there should be lots - it might take a few to find one that is truly complete with drill Letters, Numbers, and fractional sizes to decimal inch sizes.
The note TAP 3-48 refers to a thread size spec that is required for the hole. Again the drill and tap chart should have the drill and hole sizes etc. Usually the tap information is on the bottom for the size chart.

 
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