If you do not like how the Number custom field is displaying in Jira (for example, if you do not want it to display the commas), you can modify a velocity file to configure this. In particular, look at the file WEB-INF/classes/templates/plugins/fields/view/view-number.vm. As mentioned here:

At the moment to change the way the numbers are printed the easiest thing to do is to edit:
WEB-INF/classes/templates/plugins/fields/view/view-number.vm
under the JIRA web application and replace:
$!numberTool.format($value)
with:
$value.longValue()

and restart.

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http://support.atlassian.com/browse/JSP-20302 
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