Lenz - Nostrali level sight windows indicate oil or fluid level in your gear box, gear reducer, axles, and reservoirs. The hex body bushings are available in brass, aluminum, and stainless steel. The lens of sight windows can ordered in Grilamid or glass. Standard threads are (G) BSPP, (R) BSPT, and Metric. Please select the correct thread sealing washer for your application if you are using BSPP or Metric threads. SAE or NPT threads are available upon request if quantities are large enough. Operating temperature ranges are from +14 F to 482 F depending upon the configuration. All sight windows are R.O.H.S. and R.E.A.C.H. compliant.