Hi everyone!
Recently I foundout a leaf chain which consist of central thick links along the centerline of the chain (e.g. in the above forklift). What is the purpose of this central thick link (is it just a spacer or it has a load function) ? What material this link is made (metal/plastic/other)? How this kind of chain is designated (leaf combination notation)? Where can I find an additional information about this kind of chain (manufacturers, internet sites etc.)

Also, I am looking for metric standard dimemsions for forks. Is there any metric forks? where I can find a table/cataloge of metric forks measurements?
Thank you.