Mitragyna speciosa is an evergreen tree that can grow to a height of 25 m (82 ft) tall and the trunk may grow to a 3 ft (0.91 m) diameter. The trunk is generally straight and the outer bark is smooth and grey.
Overall though, metal is a much better option than plastic. In most cases, it is much more effective and reliable, and the right choice of metal will avoid the pitfalls of rust or weakness. Aluminium, steel and stainless steel are the three metal gutter materials for guards that homeowners can choose from.
1 Ceramics are also more chemically resistant and can be used in wet environments where steel bearings would rust. 2  The major drawback to using ceramics is a significantly higher cost.3  In many cases their electrically insulating properties may also be valuable in bearings. Ceramics such as alumina and boron carbide have been used in ballistic armored vests to repel large-caliber rifle fire. 2  Such plates are known commonly as small-arms protective inserts (SAPI). 3  Similar material is used to protect cockpits of some military airplanes, because of the low weight of the material.