Definition
Full Hole Connection — A Full Hole (FH) connection is an API rotary-shouldered connection designed with a large internal bore to maximize fluid flow through the connection, historically used on drill pipe and collars where hydraulic efficiency matters.
Also known as: full hole connection, FH connection, full-hole thread
What Full Hole means
The Full Hole (FH) connection is one of the original API rotary-shouldered connection families, named for its relatively large internal diameter that keeps the flow path through the tool joint open — a “full hole” for drilling fluid. This large bore reduces pressure loss and erosion compared with more restrictive designs.
FH connections are identified by the pipe size, for example 4-1/2 FH or 6-5/8 FH. Some FH connections are dimensionally interchangeable with NC connections (e.g., 4-1/2 FH relates to NC50-class geometry), which the NC series was created to consolidate.
Where it fits
- Hydraulics — the wide bore favors high circulation rates and lower standpipe pressure.
- Legacy strings — FH remains in service and inventory, though many modern strings use NC.
- Single shoulder — like other classic API connections, FH is single-shouldered.
Renting FH-connection tubulars
Full Hole connections still appear across drill pipe and collar inventories. We can supply drill pipe and drill collars with FH or the interchangeable NC connections your string requires — contact us to verify make-up compatibility.