The usual weapon used in Kendo is the shinai. It is constructed of 4 pieces of split bamboo. The tip of the shinai is covered in leather; the four staves are held apart by a t-shaped piece of rubber. The staves are held together at the opposite end by a long leather handle. The handle is round rather than oval like a real katana. A leather lace tied in a complicated knot about a third of the way from the tip keeps the staves from spreading too far apart. A string runs down one stave -it signifies the dull edge, or back of the sword. The split construction allows the staves to both flex and compress against each other, absorbing much of the energy of the blow. Attacks which miss the armour cause bruises; nothing more. Poorly maintained shinai can be dangerous - bamboo shinai must be checked and sanded regularly to avoid splinters, and oiled or waxed to help prevent drying out and subsequent breakage. For this reason carbon fibre shinai have become popular. Although expensive and less lively-feeling compared to bamboo, they are virtually maintenance free and last for years. Also, carbon fibre shinai may be purchased with an oval grip, which many people prefer. Previously, only expensive hand-made bamboo shinai had oval grips.