For pressures not exceeding 125 pounds per square inch mountings with screwed ends not exceeding 1 inch may be used; the screwed portion of any such mounting being an integral part thereof and the thickness at the bottom of the thread being not less than 3/16 inch.

The mountings may be screwed:-

Directly into the boiler shell plate, nuts being fitted on the waterside, or into steel distance pieces the length of thread engaged being in no case less than the bore of the mounting plus ¼ inch.

The distance pieces shall be made from solid mild steel. They shall be screwed into the plate and fitted with nuts on the water side. The walls of the distance pieces shall be not less than ¼ inch thick at the bottom of the thread.

Mountings may be attached directly to any shell or end plate where the plate is of sufficient thickness to allow a suitable surface to be obtained for the attachment of the boiler mounting.

The minimum thickness at the hole in the shell or end plate shall be not less than the thickness required for the maximum permissible working pressure considering the plate as being unpierced.

Where the boiler mountings are secured by studs the studs shall have a full thread holdings in the plate for at least one diameter. If the stud holes penetrate the whole thickness of the plate, the stud shall be screwed right through the plate and be fitted with a nut inside having a thickness equal to the diameter of the stud. Where bolts are used for securing mounting they shall be screwed right through the plate with their heads inside the shell or end plate.

Where standpipes are used, the flanges shall be machined or flame-cut by machine on the edges. The bolting flanges shall be machined on the jointing and bolting surfaces.

Where saddles are used, the edges of the flanges shall be machined or flame-cut by machine. The jointing surfaces shall be machined. The studs for the attachment of the mountings, if screwed through the saddle, shall be fitted on the inside with nuts of full thickness.

Where the stud holes do not penetrate through the saddles the length of the screwed portion of the stud in the plate shall be not less than the diameter of the stud.

Where pads are used, the joining surfaces shall be machined. The pads shall have sufficient thickness to allow the drilling of the stud holes for mountings without the inner surface being pierced and the length of the screwed portion of the stud in the pad shall be not less than the diameter of the stud.