Tubular Chair Marcel Breuer style  

Hi all, I am new to this forum. Today we bought some nice tubular chairs for our new appartment. The seller said he  bought them in the seventies. We just wanted to use them as normal chairs because we like the design. So we cleaned them (taking apart, cleaning leather and tube) and then we noticed a mark (see pictures). It says 3A on one side and 287 on the other side. Does anyone know who made these? Thank you in advance!

Ps: if i figure out how to attach more pictures, I will.