difference between union vs. coupling

What is the difference between a union and a coupling (I saw a union has a nut in the middle)? Also, is there a compression fitting to join two pieces of 1/2 inch copper pipe? I am adding a section for my new laundry sink, and would prefer to avoid sweating them if I can. Thanks.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 12/28/04 "Eric and Megan Swope" snipped-for-privacy@verizon.net asks in part

nut in the middle)?
The nut in the middle allows the fitting to be taken apart without disturbing the soldered or threaded joints on either end.

pipe?
Yes, look for a 5/8 compression union.
Doug
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.