millimeters? All the PCBs I've ever done have hole sizes in fractions of inches! ;-)
Hole sizes are a combination of size needed to fit component leads and drill bits offered by the fabricator. For example, a number of the "prototype" PCB vendors (the kind you email your Gerbers to along with credit card number) have a limited selection of drill sizes in order to keep things standardized and keep their costs down (and hence keep down the cost to you). Thus, you may need to adjust the hole sizes on your PCB to fit their available sizes.
Other places, such as my current employer, seem happy to let you use any and every conceivable drill bit (in increments of 0.0005") all on the same PCB.
If you're doing your own PCB, make a set of reasonable choices. Avoid using a hole that is "just big enough" as it makes it hard to remove a component. You'll find that you need only a few sizes for the normal range of components.
Hole sizes are a combination of size needed to fit component leads and drill bits offered by the fabricator. For example, a number of the "prototype" PCB vendors (the kind you email your Gerbers to along with credit card number) have a limited selection of drill sizes in order to keep things standardized and keep their costs down (and hence keep down the cost to you). Thus, you may need to adjust the hole sizes on your PCB to fit their available sizes.
Other places, such as my current employer, seem happy to let you use any and every conceivable drill bit (in increments of 0.0005") all on the same PCB.
If you're doing your own PCB, make a set of reasonable choices. Avoid using a hole that is "just big enough" as it makes it hard to remove a component. You'll find that you need only a few sizes for the normal range of components.
When I was little the neighbours had a daughter, with 12 toes and 12 fingers... bet she'd learn to count and measure just fine in the USA... the rest of us use metric... I Know they tried it for 2 weeks in the US, but gave it up because it was too hard 
.
For 89.7% of the stuff you'll do, you need th 0.8mm bit.
.For 89.7% of the stuff you'll do, you need th 0.8mm bit.
peranders said:
Never heard of millimeters?1 inch = 25.4 mm. My pcb fabricator can offer just about any hole size so I just have to pick the size I want. More than 10 different sizes is not a problem. If you make a doublesided board 0.9 mm is very suitable for 0.6-0.8 mm leads.
who's your fabricator BTW?
Milimeter
http://www.crownhill.co.uk/level3.php?cat=17&sec=8&PHPSESSID=e1ee8daed751ac49adaca0f3230738fc
In the past, yes in US, they use measuring in Inch unit but in Europe use in metric.
In Asia some mixed up from difference source, but now most of electronics semiconductor become small and smaller, measuring unit changing to Metric
I do not know exactly in US.
U.S. UNION TOOL, INC.
You can find out
In Germany, Kammer news reports that they finish to develop
0.03mm drill bit, you can see how small.
http://www.mpk-kemmer.de/KemmerTechnologyAG/KemmerNews/Kemmer_news_02-05_engl.pdf
In Japan and Chaina, seem all of them supply drill bit in Metric unit.
http://www.crownhill.co.uk/level3.php?cat=17&sec=8&PHPSESSID=e1ee8daed751ac49adaca0f3230738fc
In the past, yes in US, they use measuring in Inch unit but in Europe use in metric.
In Asia some mixed up from difference source, but now most of electronics semiconductor become small and smaller, measuring unit changing to Metric
I do not know exactly in US.
U.S. UNION TOOL, INC.
You can find out
In Germany, Kammer news reports that they finish to develop
0.03mm drill bit, you can see how small.
http://www.mpk-kemmer.de/KemmerTechnologyAG/KemmerNews/Kemmer_news_02-05_engl.pdf
In Japan and Chaina, seem all of them supply drill bit in Metric unit.
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