607 datasheet(42/60 Pages) ABBATRON

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Spacer and Standoff Information

Spacers are mechanical devices used to physically or electrically

separate board, chassis, components and other devices from each

other. They may also be used to locate, hinge and guide parts in

electrical and mechanical assemblies. They are not intended to be

used as precision bearings or shafts or as highly precise jacking or

adjusting devices.

Materials:

Brass: Is the most common material for high quality spacers. It

provides strength, corrosion resistance and electrical conductivity.

It is non-magnetic and will stand up well to most environmental

conditions, including heat and humidity. The weight of larger brass

spacers can be a disadvantage in certain situations.

Aluminum: Spacers provide a compromise between weight and

strength. Although they cannot be provided in solderable finishes,

they can be plated with special colored finishes besides the standard

clear chromate. Anodized finishes have insulating characteristics

when undamaged, and can be provided in a black matte, non-reflec-

tive surface. Aluminum is non-magnetic and can withstand severe

conditions when properly finished.

Nylon: Is a general-purpose insulating material for spacers. Molded

threads are precise and will withstand torquing without stripping.

It is an excellent insulator and its surface lubricity allows wires to

be routed against the spacer without fear of chafing the insulation.

Disadvantages of nylon are relatively low operating temperature,

cold-flow under high-compressive loading and a tendency to absorb

up to 2% moisture in high humid ambients.

Phenolic: Are made from paper-base, resin impregnated, heat-cured

materials. High torque should not be applied to these spacers. They

are the insulating spacer of choice when higher temperatures are

encountered than can be withstood by nylon, or where greater

strength without cold-flow is required.

Ceramic: Spacers are a Grade L-5 Steatite material, glazed and fired

at high temperature. They exhibit exceptional strength in compres-

sion and tension, but are quite weak in shear and torsion, as are

all glass-type materials. Ceramic spacers will withstand very high

operating temperatures and very high voltages without flash-over.

Due to the nature of the manufacturing processes, high tolerances

cannot be met in dimensions or threading, so these spacers should

not be considered as precise devices. Tightening torques on fas-

teners should be held to a minimum and no shear or torsional load

should be applied to spacers in use.

Alternate materials such as Stainless Steel are available in quantity

from the factory. Call for details.

Shape: Standard spacers are offered in round or hex external form.

Other forms can be supplied in quantity as specials from the factory.

Round spacers are generally used for minimum clearance require-

ments and as a general use shape. Hex spacers are used primarily

in threaded spacers where wrench use and tightening are required.

For this reason, hex spacers are only offered in threaded styles, while

round spacers are offered in clearance and threaded types.

Diameters: Outside diameters are graduated with regard to in-

ternal thread sizes for strength, minimum clearance requirements

and footprint area. In general, a minimum of two thread sizes are

provided for each OD. For specifications not illustrated in the fol-

lowing pages, contact the factory or your sales representative for

more information.

Length: Standard spacers are generally offered in lengths of 1/8” to

1”. Extended length spacers are available up to six inches in gradu-

ated half and full inch increments in aluminum and ceramic only. For

metallic spacers, this is an issue of weight versus function. Brass and

steel spacers tend to be unacceptably heavy in the longer lengths

and serve no purpose which cannot be met by aluminum. Ceramic

spacers are offered in longer lengths, proportionally sized in OD for

high-voltage and high-compressive requirements.

Finishes: Various finishes have been selected as standard for each

of the materials supplied. They represent the most practical and cost-

effective finish for the majority of applications. Alternative finishes

are available on special order in quantity from the factory, including

most MIL-spec requirements.

Threading: There are three possible ways to thread the inside of a

spacer: (1) Straight through with continuous thread throughout. (2)

Halfway from each end, meeting near the middle with no continuity

of the thread throughout. (3) Part way in from each end, with no

hole through the rest of the spacer. The method used on any style

of spacer depends on the length and its ratio to the diameter of the

tap. Excessively deep threading is costly and usually not necessary.

Threads are only made continuous where practical. Please refer to

the

Thread Depth Table throughout the next section for standard

parameters. Special depths can be ordered in quantity from the

factory.

Mounting Footprint: End finish techniques of outside chamfering

and countersinking reduce the total surface area in contact with the

mounting surface of the spacers, increasing pressure at this surface.

If the area is too small, fastening pressure will cause the spacer

to dig in to the surface, deforming and possibly cracking it. For that

reason, most thread sizes are offered in two different OD spacers to

allow a choice of pressure versus clearance requirements.

HH Smith

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