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Figure 7.2 – Tool joint

In addition to these basic types, many variations of each are
available in the several drill pipe sizes and styles. Original API
tool joint, subsequently referred to as Reg. API, provided for the
bore of the pin to be much smaller than the ID of the internal upset
of the pipe which, in smaller sizes meant significant restriction to
fluid flow, but provided a strong pin.
API FH (full hole) was developed to alleviate this condition
somewhat. I was determined that by adding perhaps ¼ in. to OD of
pin. The bore could be increased as much as ¾ in. without
impairing the strength of the connection. Proprietary designs (non-
API) were next developed, having a pin bore equal to the ID of the
internal upset portion of the drill pipe. Also available for use on
external upset drill pipe is the IF (internal flush) design which has
a pin bore approximately equal to the non-upset pipe section.
All weld-on tool joints are available with either a taper
shoulder or a square shoulder for drill pipe elevators. API FH
joints can be welded onto internal upset pipe and IF joints can be
welded onto external upset pipe. Also available and currently the
most popular is an intermediate type joint welded onto IEU drill
pipe having a slight external upset plus the internal upset.

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