Specification for indicating bolts for use in public baths and lavatories
1975 Edition

As per IS 4621 (1975), indicating bolts are constructed from specified materials including aluminium alloy castings, extruded aluminium alloy, brass castings, extruded brass, and zinc-based alloy die castings. Components such as the body, knob, and spindle utilize aluminium per IS 617-1959 grades A-5-M or A-6-M, brass per IS 733-1967 or IS 292-1961 Grade 3, and zinc alloys as per IS 742-1966. The indicating disc is made from aluminium sheet IS 737-1974 or brass casting IS 292-1961 Grade 3. Gears are typically aluminium alloy casting or brass casting meeting the mentioned standards. Additionally, aluminium parts must receive an anodized coating with a minimum finish grade of AC 10 according to IS 1868-1968 to enhance corrosion resistance and durability, ensuring smooth, reliable operation in public bath and lavatory applications.

IS 4621 defines two standard sizes for indicating bolts: Size 1 and Size 2, with detailed dimensions and allowable tolerances provided in Table 1 and depicted in Figure 1 of the standard. For example, the bolt diameter (dimension A) is 12.5 mm for Size 1 and 20 mm for Size 2 with a tolerance of ±0.1 mm. Length (dimension B) ranges from 20 mm to 25 mm with ±1 mm tolerance, and overall length (dimension C) is 75 mm or 85 mm respectively, also with ±1 mm tolerance. Other dimensions such as projection length, socket diameter and depth, head height, square section size, plate diameter, and number of holes are similarly specified with precise tolerances to ensure interchangeability and proper fit. The dimension E is customized according to door thickness. These specifications guarantee consistent manufacturing quality and installation compatibility.

The IS 4621 standard mandates that indicating bolts provide a clear visual indication of occupancy status. When engaged (bolt drawn), the indicator must display the word "ENGAGED" on a red background. Conversely, when withdrawn (bolt retracted), it should show "VACANT" on a green background. This color coding ensures immediate and unmistakable recognition of whether the facility is occupied or free. Such standardized visual cues enhance safety and user convenience in public baths and lavatories.

According to IS 4621, the assembled indicating bolts must operate smoothly without any roughness or difficulty. The surface finish should be satin or bright polished to meet aesthetic and functional standards. Aluminium bolts are required to be anodized with a finish not below Grade AC 10 as specified in IS 1868-1968, which provides corrosion resistance and enhances durability. These workmanship and finish criteria ensure the bolts are not only functional but also visually suitable for public use.

IS 4621 prescribes a structured approach for sampling and conformity assessment to ensure product quality. Samples must be randomly selected from at least 10% of the packages, with a minimum of three packages involved, and an equal number of bolts taken from each chosen package. The sample size depends on the lot size, for example, up to 50 bolts require 8 samples with zero allowable defects, while lots exceeding 1,000 bolts require 125 samples allowing up to 5 defective units. Test results are rounded as per IS 2-1960 rules. A lot is accepted if the number of defective bolts does not exceed the permissible count; otherwise, it is rejected. This methodology guarantees statistically valid quality control and compliance with the standard.