FR-4

FR-4 (or FR4) is a NEMA grade designation for glass-reinforced epoxy laminate material. FR-4 is a composite material composed of woven fiberglass cloth with an epoxy resin binder that is flame resistant (self-extinguishing).

"FR" stands for "flame retardant", and does not denote that the material complies with the standard UL94V-0 unless testing is performed to UL 94, Vertical Flame testing in Section 8 at a compliant lab. The designation FR-4 was created by NEMA in 1968.

FR-4 glass epoxy is a popular and versatile high-pressure thermoset plastic laminate grade with good strength to weight ratios. With near zero water absorption, FR-4 is most commonly used as an electrical insulator possessing considerable mechanical strength. The material is known to retain its high mechanical values and electrical insulating qualities in both dry and humid conditions. These attributes, along with good fabrication characteristics, lend utility to this grade for a wide variety of electrical and mechanical applications.

Grade designations for glass epoxy laminates are: G-10, G-11, FR-4, FR-5 and FR-6. Of these, FR-4 is the grade most widely in use today. G-10, the predecessor to FR-4, lacks FR-4's self-extinguishing flammability characteristics. Hence, FR-4 has sincewhen? replaced G-10 in most applications.
Fenhar FR-4 epoxy resin systems typically employ bromine, a halogen, to facilitate flame-resistant properties in FR-4 glass epoxy laminates. Some applications where thermal destruction of the material is a desirable traitcitation needed will still use G-10 non flame resistant.
by fenharxz.com August 08, 2024
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4 seezins

One of two white rappers named after a hotel, unless Rittz named himself after crackers instead.
People thought 4 seezins was larger than life, so he would walk out on a stage wearing stilts.
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4 seezins

The white rapper that got to take his stilts with him in jail, they liked the stilts so much.
Nobody fucked with 4 seezins in jail, that dude looked about 8 foot 20.
by The Original Agahnim June 17, 2021
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Jammin' like 4-C

It's a term commonly used to define A person who is at the top of his game.
You need To start Jammin' like 4-C G.
by Thunder Crypt May 30, 2012
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see you at 4:30

A phrase with origins from the online dating app Grindr, that is meant to cloak a confirmation for a "hookup" under the guise of common vernacular.
Male1: Are we still on for meeting in the park?
Male2: see you at 4:30
by Ed Marley June 14, 2017
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Cave 4

Do NOT enter this cave. Never do. You will regret it the moment you go in. If you go in Cave 4, you go in the pants. You become horny forever and you will not see anything the same again.
Guy 1: hey, why are you suddenly jerking off and licking feet?
Guy 2: I went to Cave 4 yesterday, it's really affected my lifestyle.
by Feathery Fag December 11, 2019
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February 4

Boy 1: hey i fucked your mom

Boy 2: Really?

Boy 1: No it’s february 4 opposite day lol
by bigbootybanna February 04, 2022
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