Cylinders are lent, not sold
A gas cylinder goes out against a deposit and is expected back, which makes it a returnable item rather than a sale. Recording the deposit against the party and the cylinder as issued means you know at any moment how many are out and with whom. Shops that treat cylinders as ordinary stock end up short by a number nobody can explain, and each one is a real cost.
Electrodes by kilo and by packet
Welding rods sell in sealed packets and loose by weight, in several grades and diameters. Grade and size belong on the item because using the wrong rod is a job failure your customer will attribute to you. Holding the unit and conversion means both packet and loose sales come from the same stock with the figure staying honest.
Machines and warranty
Welding machines and cutting equipment carry warranties and come back for service. Recording model and serial on the invoice means the claim is traceable and the manufacturer honours it, and it gives you a service history that a repeat sale is built on. Without it, a replacement under warranty comes out of your own margin.
Fabricator running accounts
Your regular customer is a fabricator drawing rods, discs and gas through a job and settling at the end. High frequency, small amounts, and a running account that grows quietly. A credit limit set at the start and a monthly statement are what keep it from becoming a problem, and the ledger maintains itself from the billing.