求翻译：轻钢龙骨顶棚骨架施工，先高后低，主龙骨间距和吊杆间距一般在900mm-1100mm控制，特殊情况不得大于1200mm，次龙骨间距一般为450mm×450mm左右，或按饰面板的规格选定，（可外露龙骨）吊杆直径通常为8mm，吊杆应垂直吊挂，旋紧双面丝扣，外露铁件必须刷二度防锈漆，离墙边第一根主龙骨距离不超过200mm，排列最后距离超过200mm应增加一根。是什么意思？

Light steel keel ceiling skeleton construction, first high Hou low, main keel spacing and hanging Rod spacing General in 900mm-1100mm control, special situation shall not is greater than 1200mm, times keel spacing General for 450mmx450mm around, or by ornaments Panel of specifications selected, (can exposed keel) hanging Rod diameter usually for 8mm, hanging Rod should vertical hanging, Rotary tight duplex silk buckle, exposed iron pieces must brush II of paint, away from wall edge first root main keel distance not over 200mm, arranged last distance over 200mm should increased a root.