For an Oldham coupling used between two shafts, which among the following statements are correct?

I. Torsional load is transferred along shaft axis

II. A velocity ratio of 1:2 between shafts is obtained without using gears.

III. Bending load is transferred transverse to shaft axis.

IV. Rotation is transferred along shaft axis.

To determine the correct statements regarding an Oldham coupling, let us analyze the function and characteristics of this mechanical component:

An Oldham coupling is a type of flexible coupling used to connect two parallel shafts that have a lateral offset (misalignment) between their axes. The coupling consists of three main elements: two outer flanges (hubs) keyed to the driving and driven shafts, and a central floating disc that interfaces with both flanges via tongue-and-groove joints oriented perpendicular to each other.

Let us evaluate each of the given statements:

Statement I: Torsional load is transferred along shaft axis.
This statement is correct. The primary purpose of any shaft coupling, including the Oldham coupling, is to transmit torque (torsional load) from the driving shaft to the driven shaft along the general longitudinal axis of the shafts, enabling rotation to be passed from one to the other.

Statement II: A velocity ratio of 1:2 between shafts is obtained without using gears.
This statement is incorrect. An Oldham coupling connects two shafts to transmit rotation at a constant velocity ratio of 1:1. The input and output shafts rotate at the exact same angular velocity; it does not function as a speed reducer or multiplier.

Statement III: Bending load is transferred transverse to shaft axis.
This statement is incorrect. Flexible couplings, including Oldham couplings, are designed specifically to accommodate misalignment (such as lateral offset) without transmitting bending moments or significant transverse bending loads between the shafts. By allowing sliding movement of the central disc, the coupling isolates the shafts from bending loads rather than transferring them.

Statement IV: Rotation is transferred along shaft axis.
This statement is correct. The coupling transmits the rotary motion from the input shaft to the output shaft along the aligned/parallel shaft axis system.

Therefore, statements I and IV are correct, which corresponds to the option "I and IV".