Apeiriannaucrew, alsosom amannanreferredtoasamachinebolt, isascrewthatistypicallydesignedtobe
fastenedtoanexisting, tappedholeonametalsurface, fel arferinconjunctionwithacorrespondingnut.
Thesetypesofscrewsarenotaslargeastheaveragescrew, fel arferranginginsizesuptothreequarters
ofaninch (19.05mm) buttheycanstillbelarger.Variationsbetweenmachinescrewsmainlyexistinoverall
maint, siâp siâp, slottype, hyd, deunydd, a nodweddion nodwedd.
Amajorwayofcategorizingamachinescrewisbythetypeofslotinthehead, whichwilldeterminethekind
ofscrewdriverthatistodriveitintoitshole.Thetwomajorkindsofscrewdriversusedwithmachinescrews
areslottedandPhillipsheadscrewdrivers, butthereareseveralotherminortypesofscrewdriveholessuch
asTorx six-pigfain, seren-shapeddriveholes thatrequiremorespecializedscrewdrivers.Specialized
mathau o sgrewdriveholesmaybeimportantwhenitisdesiredthatthescrewsarenotinterferedwithfor
safereasons, sinceitismoredifficulttoacquirespecializedtypesofscrewdrivers.Adangerouselectrical
panel, forinstance, isagoodplaceforamachinescrewwithaspecializedtypeofhole.Othermachinescrew
headscanbesimilartoahexorsquareboltthathavenoscrewdriverslotandmustbeturnedwithawrench.
Theshapeoftheheadofamachinescrewwilldeterminehowitliesonceitisfastenedtoahole.Roundand
panheadswillprotrudefromaflatsurfaceoncetheyareattached.Flat-headedscrewsaredesignedforholes
thatareboredsotheylayflushwiththesurfacewhentheyhavebeenscrewedin.Theheadofasetmachine
screwissmallerthanthediameterofthescrewthreads, sowhenitisattacheditcanbedriventhroughahole
andadjustedtoadesireddepth.
Moreofthemajordifferencesbetweenmachinescrewsareinthecharacteristicsofthethread.Thispartof
anygivenmachinescrewisoneofthemostimportant, becausethecorrespondingholesthattheyare
fastenedtowilltypicallybetappedtofitonlyonespecificsizeandtypeofscrewthread.Thesystemusedfor
safonau nodweddudifferentthreadsusuallyfollowsISO (InternationalOrganizationforStandardization),
whichhavebeenestablishedtokeepconsistentdesignspecificationsinmachinepartsproducedthroughout
theworld.Twoofthemajorthreadcharacteristicsareitsdiameterandpitch, thelatterbeingthedistance
betweenthreads.Thesescrewthreadscanalsobemadetobescrewedclockwise (llaw dde) neu
gwrthglocwedd (llaw chwith).
Er bod hyn yn digwydd yn fecanyddol, yn berthynol i bob pwrpas, yna bydd y rheiny yn cynnwys mesuriadau
betweensize, shapeandlength, mostlydeterminedbytheirintendedpurposeandhowstrongtheyneedtobe.
Gall Pringmetal gynhyrchu'r rhan fwyaf o sgriwiau peiriant fel y soniwyd amdanynt hefyd, hefydCustom-madescrewscanalsobemanufacturedforspecificmachinesthatdonotevenhavetofollowany
Safonau ISO.Sgriwiau peiriannaucanbemadeofanyofavarietyofmetalsorplastics.