Think Twice Before Purchasing GO/NOGO Medical Screw Thread Gages?
I know that this is an odd thing for a Screw Thread Gage Salesperson to say, but maybe even think three or four times. Consider very carefully if GO/NOGO Medical Screw Thread Gauges are a wise selection of tool for this task. For plastic components, we think not, and that there is an alternative which will better meet the in-production or incoming material inspection task. For metal components, we think that a specially designed screw thread gage may be developed specifically for the nuisances of your particular part.
Are Screw Thread Gages Mandated?
A review of medical connector specifications in ISO18250 and ISO 80369 (and the obsolete ISO 594-1 and ISO 594-2) finds no requirement for use of GO/NOGO Screw Thread Gauges for validation of the connectors. If we were to suggest the use of screw thread gauges we would only suggest their use for monitoring production or for in-coming inspection; however, we think that there is an alternative which will better meet the in-production or incoming material inspection task.
The Medical Screw Threads Unusual
These screw threads are a little different than the common UN-Series or the M-series screw threads. The Medical Community has decided to think outside of the box and has designed the Medical Connector Screw Threads so they bear very little resemblance to any of the screw threads currently listed in standard industrial screw thread specifications. The medical screw thread is well designed to meet its purpose, but it also causes several problems related to gauging the screw thread size. The problem which needs to be mentioned here is that because of the design of the threads, standard screw thread gages nearly impossible to manufacture.
Fitment Screw Thread Gauges Function Differently
To overcome the screw thread gauge manufacturing problem, the screw thread gauges used for medical connectors are designed to test 'fitment'. What this means is that the medical connector screw thread gages do not test the size and form of the screw thread to the specification; rather they test to assure that the screw thread can be assembled to its mating connector. Passing the screw thread gage test assures that the screw thread will assemble in the field, but it does not assure that the screw thread is within dimensional compliance to the specification. Fitment gages will test to assure that the parts will fit with an appropriately sized mating part, but the gages may pass an out of tolerance part. Assembly is the most important end result of medical connectors screw threads because they carry no load and have little possibility of failing under stress. This is not considered a critical fault because everyone is happy if the parts fit together.
Should You Use Screw Thread Gages?
There may be a push made by someone in your company to begin using GO/NOGO Screw Thread Gauges to test your products. Before you purchase you should be aware that...
Screw Thread Gages Are Not Returnable
These GO/NOGO Fitment Screw Thread Gages are specially made per order. Once the order is placed, cancelling it may incur a cancellation fee up to 100% of the order value. If on receipt of the GO/NOGO Screw Thread Gauges they are not returnable for any reason. We can assure that if there is a problem with the gage, the manufacturer will work to resolve the problem, but there are some problems which cannot be resolved.
The gages are hardened steel with some sharp edges which may mar the parts as they are tested. We have procedures to mitigate this situation, but it cannot be eliminated.
The GO gage is very difficult to use. The screw thread has only a quarter turn of engagement. A normal thread has multiple turns, which allows the GO gage the opportunity to engage the thread. A quarter turn is very fast and there is no room for adjustment of the GO gage to the part, making it difficult to align the gage to properly fit the GO gage. The gage does not have a conical guide to assist the alignment.
The NOGO gage is more difficult to use than the GO gage. The normal use rule for a NOGO gage is that it passes the part if the gage engages the thread not more than 2 turns. With only a quarter turn of part screw thread engagement, the NOGO gage cannot even be allowed to start on the thread. It is difficult to determine if the part is to size, or if there is a problem with assembly of the gage to the part. The gage does not have a conical guide to assist the alignment.
A Special Feature of the Plug Gages
The plug gages offered will have a C’Bore designed to clear the male cone.
A Special Requirement of the Ring Gages
What we offer are GO/NOGO Fitment Ring Gages made using AGD (American Gage Design) ring gauge blanks. This ring gauge design requires the use of a Set Plug Gage to master the ring gauge. The purchase of one Set Plug Gage is Mandatory for the initial purchase of one of each size of these ring gauges. Once you own the Set Plug Gage for a specific size ring gauge; that Set Plug Gage can be used to master additional copies of that same size ring gauge. On or quotation for these ring gages we will offer the Set Plug Gauge as the mandatory item. If you already own a Set Plug Gage for the size you have requested; it must be provided at the time of order for the gauge maker to use to master your new purchase. There will be a calibration fee because the gage maker must validate the Set Plug Gauge has not been worn out and is acceptable for use as a master. All of this can be discussed with the salesperson making the quotation for your new ring gage.
For Plastic Parts The Alternative We Recommend:
We suggest using a Reference Connector to test the thread for general acceptance on incoming inspection or during production. The Reference Connector has the cone to assist in aligning the connector for assembly to the thread. This is a simple pass/fail test. either it assembles or it does not. The screw thread in the reference connector is made to the connector mean, so it is not valuable for testing the screw thread limits, but it will alert on a catastrophic failure of the thread. It is expected that small deviations from the standard will have no impact on the assembly to mating pieces, so testing for this is not a good use of resources. We expect that any failure noticed will be a catastrophic failure, one which will inhibit in-use assembly. We recommend the reference connector used for Stress Cracking Test. There is no dimensional reason for this selection, but rather the Reference Connector used for Stress Cracking is the most popular reference connector, thus more likely to be available from your inventory, or if not, it is more likely to have an alternate use in your facility at some later date.
For Metal Part Testing We Recommend:
We suggest keeping your cutting tools sharp and changing them often to assure an acceptable screw thread form and then, like the plastic part, use a Reference Connector to test the screw thread for fitment at the machine during production to identify catastrophic failure. If it is determined that proper GO/NOGO Screw Thread Gauges are a must, then we can work with you to develop a set of gages which will test the parts you are manufacturing. The parts you are manufacturing will have a form and tolerance which is within the official requirements but is more restrictive. By defining the more restrictive form and tolerance; gages should be able to be produced, unless your form is to the specified extreme. To make GO/NOGO Screw Thread Gages we suggest your part have symmetrical flank angles and must have MIN/MAX pitch diameters. The major and minor diameters will be set by the specification. With this information we should be able to get a set of gages made. The lead-time will be a minimum of 8 weeks. The above Problems #2 and #3 will exist, so the gages will not be easy to use and will require special use instructions. The GO/NOGO Screw Thread Gages made for testing your metal parts, made to your unique design, will not be useable to test the general medical connector screw thread.
This data is provided for general information only. The intention is to provide accurate information; regardless; errors may exist in the supplied information. If accuracy is critical, base your final decisions on the data provided in the root documents: ISO 594-1; ISO 594-2; ISO 18250 and ISO 80369; which are copyrighted documents. To purchase a copy of an engineering document visit an Authorized Reseller.
Original Posting: 2/24/2015
Last Revision: 4/20/2020
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