We are professional manufacturer of stretcher bars and stretcher frame , the frame is four singles assembled together , the normally wood for the frame is pine wood or paulownia wood , pine wood the wood is much heaveier,the bar is not easy to bend , paulownia wood because it grows very fast , the density is very low , so the paulownia is very light , if you can dry the paulownia well , the wood also very good , but it is not suitable for longer stretcher bar or the bigger size frames , it too large still has the risk of bend , we have been in the stretcher bar producer for about 20 years , so we can control the quality very well from the raw wood selection to finally assembled frame , not every customer needs to assembled the frame , some just buy the wood bars , because the assembled frame occupies a lot of space , this will add the shipping cost , especially this year 2021 , the shipping cost to America East max 27000$ , it is a huge amount , because the total amount of one 40ft HQ stretcher bars cost not high .