Being a retired engineer I always recon to have a good eye for measurements. so when I bought these spacers from wickes I had my doubts about their accuracy so stuck a couple in a pair of digital calipers. The 1mm spacer measured 1.72mm and 2mm spacer measured 2.42mm, so if you want a 2mm grout line you would be nearer by using a 1mm spacer. Think it might be worth buying some better quality ones.