| bolted rigid frog | A frog build entirely of rolled rails, fillers between the rails and rigidly held together with bolts. |
| clamp frog | A frog built of rolled rails, fillers between the rails, and held together with clamps. |
| spring rail frog | A frog having a movable wing rail held against the point rail by springs, normally presenting an unbroken running surface to wheels using one track while the flanges of wheels on the other track force the wing rail away from the point rail to provide opening. |
| spring rail frog, right hand and left hand | Standing at the toe end of the frog and looking towards the point, the right-hand spring frog has the spring wing rail located on the right-hand side, and the left-hand spring rail frog has it located on the left-hand side. |
| railbound manganese steel frog | A frog consisting of a manganese steel center casting fitting into and surrounded by rolled rails and rigidly held together with bolts. |
| self guarded frog (flange frog) | A frog provided with a guard member for guiding the flange of a passing wheel past the point of the frog by engaging the tread rim of the wheel in a horizontal plane above the top of running surface of the frog. |
| frog angle | The angle formed by the intersecting gage lines of a frog. |
| frog number | One-half the cotangent of one-half the frog angle, or the number of units of center line length in which the spread is one unit. |
| heel end of frog | The end of a frog farthest from the switch and where the running surfaces, diverging from the point, terminate. |
| toe end of frog | The end of a frog in front of the point and towards the switch. |
| heel spread | The distance between the gage lines at the heel end of the frog. |
| toe spread | The distance between the gage lines at the toe end of the frog. |
| throat of frog | The point at which the converging wings of a frog are closest together. |
| frog point | The part of a frog lying between the gage lines extending from their intersection to the heel end. |
| point of frog, theoretical | The point of intersection of gage lines of the frog. |
| point of frog, half-inch | A point located at a distance from the theoretical point towards the heel and equal in inches to one-half the frog number and at which the spread between the gage lines in one-half inch. It is the origin from which shop measurements are made. |
| point of frog, actual | A point at which the spread between the gage lines is sufficient to allow for a practical width of manufactured point. |
| guard point | The point formed by guards introduced or extended into the toe portion of a frog. |
| heel length | The distance between the heel end and the half-inch point of a frog, measured along the gage line. |
| toe length | The distance between the toe end and the half-inch point of a frog, measured along the gage lines. |