Pocket Guide to Flan..

to as an all-thread or close nipple by the craftsmen.
Other nipples are described in size by the nipple's
length. A shoulder nipple is an all-thread nipple with a
small unthreaded section in the center of the nipple
forming a shoulder. Some nipples have a thread on one
end only. Some used with socketweld fittings do not
have any threads. Store nipples by type, size, and
length.
Swage nipples are used to reduce pipe sizes. Swages
are available in combinations from Vs-in. to about 8-in.,
but larger in special cases. Figure 6-5 shows a typical
swage nipple threaded on both ends. Swages may have
almost any combination of ends such as bevel large end,
thread small end, grooved, and bevel both ends.
Another type of cross-over fitting is the sub-tubing nip-
pie as shown in Figure 6-6. Sub-tubing nipples are used
to change from an API tubing thread to a line pipe
thread. The longer variations of this nipple are called
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Figure 6-5. Swage Nipples. (Courtesy of Jaqua-McKee, Inc.)