ss open-hearth steel
tubes of No. 10 B. W. G. where the boilers are built for working
pressures up to 210 pounds. Where the working pressure is to be above
this and below 260 pounds, No. 9 B. W. G. tubes are supplied.

[Illustration: Inside Handhole Fittings Wrought-steel Vertical Header]

The tubes are expanded into headers of serpentine or sinuous form, which
dispose the tubes in a staggered position when assembled as a complete
boiler. These headers are of wrought steel or of cast iron, the latter
being ordinarily supplied where the working pressure is not to exceed
160 pounds. The headers may be either vertical or inclined as shown in
the various illustrations of assembled boilers.

[Illustration: Wrought-steel Vertical Header]

Opposite each tube end in the headers there is placed a handhole of
sufficient size to permit the cleaning, removal or renewal of a tube.
These openings in the wrought steel vertical headers are elliptical in
shape, machine faced, and milled to a true plane back from the edge a
sufficient distance to make a seat. The openings are closed by inside
fitting forged plates, shouldered to center in the opening, their
flanged seats milled to a true plane. These plates are held in position
by studs and forged-steel binders and nuts. The joints between plates
and headers are made with a thin gasket.

[Illustration: Inside Handhole Fitting Wrought-steel Inclined Header]

In the wrought-steel inclined headers the handhole openings are either
circular or elliptical, the former being ordinarily supplied. The
circular openings have a raised seat milled to a true plane. The
openings are closed on the outside by forged-steel caps, milled and
ground true, held in position by forged-steel safety clamps and secured
by ball-headed bolts to assure correct alignment. With this style of
fitting, joints are made tight, metal to metal, without packing of any
kind.

[Illustration: Wrought-steel Inclined Header]

Where elliptical handholes are furnished they are faced inside, closed
by inside fitting forged-steel plates, held to their seats by studs and
secured by forged-steel binders and nuts.

The joints between plates and header are made with a thin gasket.

[Illustration: Cast-iron Vertical Header]

The vertical cast-iron headers have elliptical handholes with raised
seats milled to a true plane. These are closed on the outside by
cast-iron caps milled true, held in position by forged-steel safety
cla