What changes have occurred to the ASTM A490 specification since it was incorporated into the F3125 specification?
In December 2015, ASTM committee F16 approved the new F3125 standard, which combined six structural bolt standards, A325, A325M, A490, A490M, F1852, and F2280. The goal was to clean up inconsistencies within those various standards and combine them, so that future updates would be easier and less costly.
The goal was not to drastically change any of the requirements of the bolts, as they had been used and functioning in the marketplace for decades without major issues. However, in order to better align with each other and with current design standards, minor changes were made. The most notable change was that nut overtapping allowances were specified for the zinc aluminum coatings now allowed on A490 grade bolts. These coatings, F1136, F2833 and F3019, which have subsequently been combined into F3393, are thinner than hot-dip galvanizing, but thicker than electro-zinc plating, so special overtapping allowances were needed to alleviate the thread fit issues that were being experienced. The table below shows the overtapping allowances for these coatings. Unlike hot-dip galvanizing, where overtapping is performed after coating, overtapping for F3393 is done prior to coating. Please note, proof loading of the nut is required after overtapping to assure the nut has the structural integrity for use with A490 grade bolts.
|Overtap Allowance Before Coating, inches
|Overtap Allowance After Coating
After much clamoring by the industry, a supplemental requirement was added to address alternate bolt configurations. Supplement S2 allows the purchaser to specify non-standard dimensions for thread length, head style, etc. Bolts ordered to S2 are marked with an “S” to signify that these bolts vary from the ASME B18.2.6 dimensional standard, for example A490S.