R

Radial Seal

Compression is applied perpendicular to the seal centerline.

Reciprocating Seal

Seals used in moving piston and rod situations.

Reinforcing Agent

Fillers, such as Carbon Black, added to the elastomeric batch mix to improve such physical properties as tensile strength.

Resilience

The capability of returning to original size and shape after deformation.

RMA

Rubber Manufacturer's Association.

RMS

Root Mean Square. A measure of surface roughness typically applied to the machining of metal gland and shaft surfaces. RMS stands for the square root of the sum of the squares of micro-inch deviation from true flat.

Rotary Seal

Seals for rotating shafts, with the turning shaft protruding through the I.D. (hole) of the O-ring.

Rubber

A common name for both naturally occurring and synthetically made elastomers.

Rubber, Natural

A natural product of the juices of certain tropical plants (latex), improved through heat treating with sulfur (vulcanization).

Rubber, Synthetic

Man-made elastomers such as Nitrile, Fluorocarbon, Silicone, etc.

Running Friction

A force which resists objects already in motion.

Runout (Shaft)

Same as gyration. When expressed in inches along, or accompanied by abbreviation "TIR" (total indicator reading), it refers to twice the radical distance between shaft axis and axis of rotation.