It is expanded flexible graphite center with braided carbon corners. The carbon corner is strong enough to avoid extrusion under high pressure while the graphite body offers good lubrication

Style 687 is available in the following cross-section range:
1/8" to 1 1/2" (3.0 mm to 38.1 mm)
 

Applications
Style 687 is suitable for steam, water, oil, solvents, alkalis, acids, and most chemicals. Exceptions are oleum, fuming nitric acid, aqua regia, and fluorine.
Style 687 is recommended for rotary and centrifugal applications. It is also excellent for valves and other static applications.