seat belt nut grade

[dan_g8]

hi, i bought some nuts off of ebay for my seat fastenings. i was told by the seller that they were grade 8 (im guessing they need to be 8 or higher) however after fully welding them onto the chassis plate and fully welding the plate onto the chassis i realised that i couldnt see a 8 stamped onto the nut. is there another way of identifying the grade of the nut? i have got a feeling that they are only grade 1!

attached (hopefully) is what is stamped onto the nut.

Dan