One specification for o-rings involves the hardness of the
substance, which relates to its ability to withstand adverse
forces in the engine. A Shore (Durometer) hardness test
remains a standard for assessing this specification, with
the Shore A scale being used for o-rings. Measurements range
from 0 to 100, with the higher the number, the harder the
substance. According to Marco Rubber, the following are the
results for this specification: ETP o-rings 78, GLT o-rings
75, GFLT 73, B 75 and F 79. To put this item in perspective,
SubsTech lists shoe heels as a 70 and shoe soles as an 80.
Strength and Elongation
strength measures the force per unit area (MPa) necessary to
break a substance, and tensile elongation measures the
percentage increase in length before breaking. For this
specification, ETP o-rings measured a tensile strength of
17.9 and an elongation of 145 percent. Other Viton o-rings
rated from 13.6 to 17.6, with elongation ranging from 140 to
an expensive rubber that offers outstanding aging properties
over a temperature range of -58°F to + 392°F.
In the reinforced state, these rubbers have relatively low
tensile strength and elongation, but these properties are
retained under a broad range conditions.
In addition to good heat and low temperature flexibility,
these rubbers also have excellent oil and fuel resistance,
low compression set and excellent resistance to ozone and
Post curing is necessary to develop optimum properties.