عنصر أنبوبي صلب يناسب بين المحمل وغطاءه، تم تصميمه في المقام الأول كسطح تآكل قابل للاستبدال داخل الجدار الداخلي للغطاء.
"76301-ps 21201,cl b specification (includes engineering type bulletins, brochures,etc., that reflect specification type data in specification format; excludes commercial catalogs, industry directories, and similar trade publications, reflecting general type data on certain environmental and performance requirements and test conditions that are shown as "typical", "average", "nominal", etc.)." test data document, steel,mil-s-5626; cadmium plated,p.s. 13101,type 2,class 2,mcdonnell douglas corp; 0.4100 in. min and 0.4300 in. max lg; 1.8100 in. min and 1.8200 in. max id; 1.9910 in. min and 1.9920 in. max od; internal flange at one end; 0.0820 in. min and 0.1020 in. max thk; 1.7550 in. min and 1.7650 in. max id; heat treat to rc 32-37 general characteristics item description