G640 Series Back Mount Redline Sight Gage - Front Viewing With Dial Thermometer

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The G640 Series back mount closed circuit sight gages provide front viewing of the fluid level clearly delineated by a redline on white background integral to the sight glass all secured within an aluminum body (HIGH-LOW markings). A wetted dial thermometer provides an analog display of the fluid temperature.

Standard Features:

  • Centerline lengths from 3 to 12 inches
  • Back mount
  • .90 inch SQ body machined from extruded aluminum bar stock
  • Fluid level visible from front of gage (.50 inches wide)
  • Viewing enhanced by redline on white background integral to sight glass
  • 2.00 inch diameter dual scale dial thermometer, 0° to 300°F and -20° to 150°C
  • Aluminum tube shields thermometer probe extending into reservoir
  • HIGH-LOW markings on aluminum body
  • 1/2-20UNF mounting studs accommodate reservoir wall thicknesses up to .75 inches
  • Suitable for use with most hydraulic and machine lubricating oils

Access to inside of reservoir is required to mount this style sight gage.

Standard Materials:

  • Aluminum construction
  • Buna N seals
  • Borosilicate glass sight
  • Zinc plated, steel hex nuts


  • Not recommended for use with steam, acidic fluids, caustic fluids and volatile fluids.
  • If aluminum construction is selected for a water application, anodizing is recommended.
  • Reservoir must be drained to remove dial thermometer or loss of fluid will occur

Pressure Rating

  • 125 psi (862 kPa) maximum operating pressure at 150°F (65°C)

Product Options

Common Modifications Available

  • Body Material: Brass, Stainless Steel or Carbon Steel
  • Seal Material: Butyl, Fluorocarbon (Viton®), Ethylene Propylene (EPDM) or Silicone
  • Centerline lengths

Custom Modifications Available

  • Sight Options: Polycarbonate or Clear Borosilicate (Ball Float Indicator)
  • Surface Treatments: Clear/Color Anodize, Zinc, Nickel or Chrome Plate
  • Fluid Level Markings: Custom Text, ISO Symbols or No Markings
  • Mounting Stud Threads: 1/2-13UNC, M12x1.75 or M10x1.50

Minimum quantities may apply.

Related Products

LDI offers several back mounted sight gages that have integral temperature monitoring of the fluid.

LDI also offers Sight Plugs for localized monitoring of fluid conditions.

Your fluid storage system is not complete until you define the reservoir.  Off-the-shelf or customized to your specifications, consider LDI your source for:



LDI - Corporate  Click for map LDI   Click for map
Precision Machining & Assembly Fabrication & Assembly
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PH: 920.682.6877                         
FAX: 920.684.7210                         



Our talented team of degreed and professionally certified Engineers, Quality Assurance, Production and Customer Service staff have many years of experience in the industry.  Their attention to detail and ability to collaborate with our clients to solve their problems is reflected in the 50+ years we have been in business.


Customer Service: 

920.682.6877, option 4

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