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Self-Guarded Frog
A frog provided with guides or flanges above its running surface which contact the tread rims of wheels for the purpose of safely guiding their flanges past the point of the frog. Separate guard rails are not required.

Shatter Cracks
Minute cracks in the interior of railheads, seldom closer than 1/2" from the surface, and visible only after deep etching or at high magnification. They may extend in any direction. They are caused by rapid (air) cooling, and may be prevented from forming by control cooling the rail. Shatter cracks also occur in other steel products.

Shimming Spikes
Long track spikes usually used to correct surface of track by placing wood shims beneath the rail and spiking through to the ties.

Shoulder
That portion of the ballast between the end of the tie and the toe of the ballast slope. Also the raised stop on a tie plate at the spike line.

Siding
A track auxiliary to the main track for meeting or passing trains.

Slip Switch, Single
A combination of a crossing with one right-hand and one left-hand switch and curve between them within the limits of crossing and connecting the two intersecting tracks without the use of separate turnout frogs.

Softwood
One of the group of trees which have needle-like or scale-like leaves. The term has no reference to the softness of the wood.

Solid Manganese Steel Frog
A frog consisting essentially of a single manganese casting.

Spiral
A form of easement curve in which the change of degree of curve is uniform throughout its length.

Splice Bars
See Joint Bars.

Split Switch with Graduated Risers
A split switch in which the switch rails are gradually elevated by means of graduated riser plates until they reach the required height above the stock rail, and therefore have a heel slope.

Split Switch with Uniform Risers
A split switch in which the switch rails have a uniform elevation on riser plates for the entire length of the switch. Since there is no heel slope, the point rail rise runs off the back of the switch in the closure rails.

Split Web
A longitudinal or diagonal transverse crack in the web of a rail.

Special Trackwork
All rails, track structures and fittings other than plain unguarded track.

Spring Frog
A frog having a movable wing rail which is normally held against the point rail by springs thus making an unbroken running surface for wheels using one track. The flanges of wheels on the other track force the movable wing rail away from the point rail to provide a passageway.

Spur
A track diverging from a main or other track connected at one end only.

Stamping
The figures and letters indented after hot sawing in the center of the rail web, parallel with the direction of rolling, indicating the serial heat number, the ingot number as cast or rolled, and one letter designating the position of each rail with reference to the top of the ingot.

Stock Rail
A running rail against which the switch point operates.

Stock Rail Bend
The bend or set which must be given the stock rail at the vertex of a switch to allow it to follow the gage line of the turnout.

Surface
The condition of the track as to vertical evenness or smoothness.

Switch
A track structure used to divert rolling stock from one track to another.

Switch Angle The angle included between the gage lines of the switch point at its point and the stock rail.

Switch Point
The tapered rail of a split switch. Also see point rail.

Switch Point Derail
A derail consisting essentially of a split switch point with the necessary fixtures.

Switch Point Guard
A short raised guard on the field side of a turnout's straight stock rail that keeps the train wheel away from the switch point which protects the thin section of the switch point from damage and prevents wheel flanges from picking any opening between point and stock rail.

Switch, Split
A switch consisting essentially of two movable point rails with the necessary fixtures.

Switch Spring
A switch with automatic spring device incorporated in the operating mechanism. This device returns the points to their original positions after the trailing wheels have passed over the flanges.

Switch Stand
A device for the manual operation of switches, or of movable center points.

Switch Tongue
Used in street track - a switch consisting of a movable tongue with a suitable enclosing and supporting body structure. Designed for use on one side of the track in conjunction with a mate or another tongue switch on the other side (a tongue switch is termed inside or outside depending on whether it is placed on the inside or outside of the curve - the outside tongue switch being comparatively little used).