Glossary P.Q.R

Pan Head  

Flat top surface rounded into cylindrical sides, and a flat bearing surface. The recessed pan head has a rounded top surface blending into cylindrical sides and a flat bearing surface.  


A process of surface treatment for neutralizing stainless steels. An n oxidizing solution, such as nitric acid is applied to the surface. This strengthens the normal protective film which helps in resisting corrosion. It also removes any foreign substance which might cause local corrosion.  

Pattern Nuts  

Special nuts usually furnished in plain or chamfered face unless otherwise specified, and threads are unified Coarse or unified Fine, Class 2B. (also small and extra small)  


The stretching of metal by hammering or rolling the surface.  

Phillips Recessed Head  

A type of screw drive having a cross recess with a wide center opening, steep walls and a blunt conical bottom. Permits easy and rapid entrance of the 4-winged driver.  

Physical Properties  

Those properties familiarly discussed in physics, including those described under mechanical properties; for example, density, electrical conductivity, co-efficient of thermal expansion.  

Pinch Point  

A sharp conical point, usually of 45 degrees included angle, formed by a pinching operation.  

Pipe Caps  

A cap that threads onto a pipe (like a nut) to seal one end.  

Pipe Fittings  

The term applying to all forms of connecting parts which join pieces of pipe together.  

Pipe Plugs  

A short piece of threaded pipe, Slotted, Square Head or Socket, used to close up one end of a fitting.  

Pipe Screw Thread  

American Standard pipe threads are tapered 1 inch in 16, or 3/4 inch per foot. They are 60 degree threads, of National form with flat or rounded top and bottom.  


The distance, measured parallel to its axis, between corresponding points on adjacent thread forms in the same axial plane and on the same side of the axis.  

Pitch Diameter  

On a straight thread, the diameter of the coaxial cylinder, the surface of which would pass through the thread profiles at such points as to make the width of the groove equal to one-half of the basic pitch. On a perfect thread this occurs at the point where the widths of the thread and groove are equal.  

Pitch Line  

A generator of the cylinder or cone of a screw thread specified in the definition of pitch diameter.  

Plain Sheared Point  

The end of a fastener cut approximately flat and square to the axis, without chamfer.  

Planer Head Bolt  

A bolt having a large low square head, designed for insertion in T-slots of planer, shaper, or milling machine tables.  


This is a registered trade name owned by TR Fastenings. Plastech is assigned to our proprietary brass insert family and thread forming screw for plastics.  


The electro-mechanical coating of a metal piece with a very different metal.  


To make smooth or lustrous by friction with a very fine abrasive.  


Is a registered trade name owned by TR Fastenings. The Polymate product is 10.9 grade twinstart threadfroming screw for plastics with a 40 degree inclusive thread angle. The nominal metric thread diameter options are 2.2 through 6.0  

Precipitation Hardening  

Hardening caused by the precipitation of a constituent from a supersaturated solid solution.  

Precision Machine Screws  

Slotted machine screws, milled from bar, cut thread, and are machined finished Class 3A fits.  

Process Annealing  

Heating a ferrous alloy to a temperature close to, but below, the lower limit of the transformation range and then cooling, in order to soften the alloy for further cold working.  


(v) To perforate by pressing a non-rotating tool through the work.  


Quench Hardening  

Hardening a ferrous alloy by austenitizing and then cooling rapidly enough so that some or all of the austenite transforms to martensite.  


Rapid cooling. When applicable, the following more specific terms should be used: direct quenching, fog quenching, hot quenching, interrupted quenching, selective quenching, spray quenching, and time quenching.   


To finish a drilled or punched hole very accurately with a rotating fluted tool of the required diameter.  


Tool used for enlarging holes previously formed by drilling or boring.  

Recessed Head  

A screw head, having specially formed indentations or recesses centered on the head, into which a suitably formed driver fits.  


The amount one plane surface of a piece is set below or above another plane, usually for clearance or for economy in machining.  

Ribbed Neck Carriage Bolt  

A plain, circular, oval head bolt with a serrated neck to prevent rotation.  

Right-Hand Thread  

A thread is a right hand thread if, when viewed axially, it winds in a clockwise and receding direction.  


A headed metal fastener of some malleable material used to join parts, as metal plates, of structures and machines by inserting the shank through a hole in each piece and forming a head on the headless end.  

Rivet Bolt  

A bolt designed as a substitute for rivets, having a button head, a ribbed shank, a UNC thread, or a special thread such as a Dardalet thread or Lok-Thread (TM).  

Rockwell Hardness Test  

A measure of hardness by determining the depth of penetration of a pentrator into the specimen under certain fixed conditions of test. The penetrator my be either a steel ball or a diamond sphero- conical penetrator. The hardness number is related to the depth of indentation and the higher the number the harder the material.  

Rod Ends  

The ends of connecting rods which fit over crank pins or cross head pins.  

Roll Threading (or thread rolling)  

Applying a thread to a bolt or screw by rolling the piece between two grooved die plates, one of which is in motion, or between rotating grooved circular rolls.  

Rolled Point  

The point frequently produced by the cupping of the last 1 to 1 1/2 threads by the thread rolling pressure. This type of point is not produced intentionally but is considered as an alternative form of the plain sheared point.  


That surface of the thread which joins the flanks of adjacent thread forms and is identical with or immediately adjacent to the cylinder or cone from which the thread projects.  

Round Head  

Semi-elliptical top surface and flat bearing surface.