Sorry, I didn't do a good job at wording my post as usual. I ordered a 1um scale but received a 5um scale. Contacted the seller & he then sent me a 1um read head instead of an entire 1um scale. I contacted the seller again & he assured me that I could just swap out the 5um read head for the 1um read head. He said the glass housing is exactly the same.
I told him I wasn't comfortable doing that in case something went wrong & didn't want to be responsible, I never took one apart before. He said it's very simple & he would gladly send me another complete scale if something went wrong. He was right, was very simple & has been working fine for like 8 yrs or so now. Verified accuracy.